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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
+[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
+<!--SPDX-License-Identifier: CC-BY-2.0-UK-->
+
+<chapter id='ref-terms'>
+<title>Yocto Project Terms</title>
+
+    <para>
+        Following is a list of terms and definitions users new to the Yocto
+        Project development environment might find helpful.
+        While some of these terms are universal, the list includes them
+        just in case:
+        <itemizedlist>
+            <listitem><para>
+                <emphasis>Append Files:</emphasis>
+                Files that append build information to a recipe file.
+                Append files are known as BitBake append files and
+                <filename>.bbappend</filename> files.
+                The OpenEmbedded build system expects every append file to have
+                a corresponding recipe (<filename>.bb</filename>) file.
+                Furthermore, the append file and corresponding recipe file
+                must use the same root filename.
+                The filenames can differ only in the file type suffix used
+                (e.g.
+                <filename>formfactor_0.0.bb</filename> and
+                <filename>formfactor_0.0.bbappend</filename>).</para>
+
+                <para>Information in append files extends or overrides the
+                information in the similarly-named recipe file.
+                For an example of an append file in use, see the
+                "<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files in Your Layer</ulink>"
+                section in the Yocto Project Development Tasks Manual.</para>
+
+                <para>When you name an append file, you can use the
+                "<filename>%</filename>" wildcard character to allow for
+                matching recipe names.
+                For example, suppose you have an append file named as follows:
+                <literallayout class='monospaced'>
+     busybox_1.21.%.bbappend
+                </literallayout>
+                That append file would match any
+                <filename>busybox_1.21.</filename><replaceable>x</replaceable><filename>.bb</filename>
+                version of the recipe.
+                So, the append file would match any of the following recipe names:
+                <literallayout class='monospaced'>
+     busybox_1.21.1.bb
+     busybox_1.21.2.bb
+     busybox_1.21.3.bb
+     busybox_1.21.10.bb
+     busybox_1.21.25.bb
+                </literallayout>
+                <note><title>Important</title>
+                    The use of the "<filename>%</filename>" character
+                    is limited in that it only works directly in front of the
+                    <filename>.bbappend</filename> portion of the append file's
+                    name.
+                    You cannot use the wildcard character in any other
+                    location of the name.
+                </note>
+                </para></listitem>
+            <listitem><para id='bitbake-term'>
+                <emphasis>BitBake:</emphasis>
+                The task executor and scheduler used by the OpenEmbedded build
+                system to build images.
+                For more information on BitBake, see the
+                <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
+                </para></listitem>
+            <listitem><para id='board-support-package-bsp-term'>
+                <emphasis>Board Support Package (BSP):</emphasis>
+                A group of drivers, definitions, and other components that
+                provide support for a specific hardware configuration.
+                For more information on BSPs, see the
+                <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
+                </para></listitem>
+            <listitem>
+                <para id='build-directory'>
+                <emphasis>Build Directory:</emphasis>
+                This term refers to the area used by the OpenEmbedded build
+                system for builds.
+                The area is created when you <filename>source</filename> the
+                setup environment script that is found in the Source Directory
+                (i.e. <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>).
+                The
+                <link linkend='var-TOPDIR'><filename>TOPDIR</filename></link>
+                variable points to the Build Directory.</para>
+
+                <para>You have a lot of flexibility when creating the Build
+                Directory.
+                Following are some examples that show how to create the
+                directory.
+                The examples assume your
+                <link linkend='source-directory'>Source Directory</link> is
+                named <filename>poky</filename>:
+                <itemizedlist>
+                    <listitem><para>Create the Build Directory inside your
+                        Source Directory and let the name of the Build
+                        Directory default to <filename>build</filename>:
+                        <literallayout class='monospaced'>
+     $ cd $HOME/poky
+     $ source &OE_INIT_FILE;
+                        </literallayout>
+                        </para></listitem>
+                    <listitem><para>Create the Build Directory inside your
+                        home directory and specifically name it
+                        <filename>test-builds</filename>:
+                        <literallayout class='monospaced'>
+     $ cd $HOME
+     $ source poky/&OE_INIT_FILE; test-builds
+                        </literallayout>
+                        </para></listitem>
+                    <listitem><para>
+                        Provide a directory path and specifically name the
+                        Build Directory.
+                        Any intermediate folders in the pathname must exist.
+                        This next example creates a Build Directory named
+                        <filename>YP-&POKYVERSION;</filename>
+                        in your home directory within the existing
+                        directory <filename>mybuilds</filename>:
+                        <literallayout class='monospaced'>
+     $ cd $HOME
+     $ source $HOME/poky/&OE_INIT_FILE; $HOME/mybuilds/YP-&POKYVERSION;
+                        </literallayout>
+                        </para></listitem>
+                </itemizedlist>
+                <note>
+                    By default, the Build Directory contains
+                    <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>,
+                    which is a temporary directory the build system uses for
+                    its work.
+                    <filename>TMPDIR</filename> cannot be under NFS.
+                    Thus, by default, the Build Directory cannot be under NFS.
+                    However, if you need the Build Directory to be under NFS,
+                    you can set this up by setting <filename>TMPDIR</filename>
+                    in your <filename>local.conf</filename> file
+                    to use a local drive.
+                    Doing so effectively separates <filename>TMPDIR</filename>
+                    from <filename>TOPDIR</filename>, which is the Build
+                    Directory.
+                </note>
+                </para></listitem>
+            <listitem><para id='hardware-build-system-term'>
+                <emphasis>Build Host:</emphasis>
+                The system used to build images in a Yocto Project
+                Development environment.
+                The build system is sometimes referred to as the
+                <firstterm>development host</firstterm>.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Classes:</emphasis>
+                Files that provide for logic encapsulation and inheritance so
+                that commonly used patterns can be defined once and then
+                easily used in multiple recipes.
+                For reference information on the Yocto Project classes, see the
+                "<link linkend='ref-classes'>Classes</link>" chapter.
+                Class files end with the <filename>.bbclass</filename>
+                filename extension.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Configuration File:</emphasis>
+                Files that hold global definitions of variables,
+                user-defined variables, and hardware configuration
+                information.
+                These files tell the OpenEmbedded build system what to
+                build and what to put into the image to support a
+                particular platform.</para>
+
+                <para>Configuration files end with a <filename>.conf</filename>
+                filename extension.
+                The <filename>conf/local.conf</filename> configuration file in
+                the
+                <link linkend='build-directory'>Build Directory</link>
+                contains user-defined variables that affect every build.
+                The <filename>meta-poky/conf/distro/poky.conf</filename>
+                configuration file defines Yocto "distro" configuration
+                variables used only when building with this policy.
+                Machine configuration files, which
+                are located throughout the
+                <link linkend='source-directory'>Source Directory</link>, define
+                variables for specific hardware and are only used when building
+                for that target (e.g. the
+                <filename>machine/beaglebone.conf</filename> configuration
+                file defines variables for the Texas Instruments ARM Cortex-A8
+                development board).
+                </para></listitem>
+            <listitem><para id='term-container-layer'>
+                <emphasis>Container Layer:</emphasis>
+                Layers that hold other layers.
+                An example of a container layer is OpenEmbedded's
+                <ulink url='https://github.com/openembedded/meta-openembedded'><filename>meta-openembedded</filename></ulink>
+                layer.
+                The <filename>meta-openembedded</filename> layer contains
+                many <filename>meta-*</filename> layers.
+                </para></listitem>
+            <listitem><para id='cross-development-toolchain'>
+                <emphasis>Cross-Development Toolchain:</emphasis>
+                In general, a cross-development toolchain is a collection of
+                software development tools and utilities that run on one
+                architecture and allow you to develop software for a
+                different, or targeted, architecture.
+                These toolchains contain cross-compilers, linkers, and
+                debuggers that are specific to the target architecture.</para>
+
+                <para>The Yocto Project supports two different cross-development
+                toolchains:
+                <itemizedlist>
+                    <listitem><para>
+                        A toolchain only used by and within
+                        BitBake when building an image for a target
+                        architecture.
+                        </para></listitem>
+                    <listitem><para>A relocatable toolchain used outside of
+                        BitBake by developers when developing applications
+                        that will run on a targeted device.
+                        </para></listitem>
+                </itemizedlist></para>
+
+                <para>Creation of these toolchains is simple and automated.
+                For information on toolchain concepts as they apply to the
+                Yocto Project, see the
+                "<ulink url='&YOCTO_DOCS_OM_URL;#cross-development-toolchain-generation'>Cross-Development Toolchain Generation</ulink>"
+                section in the Yocto Project Overview and Concepts Manual.
+                You can also find more information on using the
+                relocatable toolchain in the
+                <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
+                manual.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Extensible Software Development Kit (eSDK):</emphasis>
+                A custom SDK for application developers.
+                This eSDK allows developers to incorporate their library
+                and programming changes back into the image to make
+                their code available to other application developers.</para>
+
+                <para>For information on the eSDK, see the
+                <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
+                manual.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Image:</emphasis>
+                An image is an artifact of the BitBake build process given
+                a collection of recipes and related Metadata.
+                Images are the binary output that run on specific hardware or
+                QEMU and are used for specific use-cases.
+                For a list of the supported image types that the Yocto Project
+                provides, see the
+                "<link linkend='ref-images'>Images</link>"
+                chapter.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Layer:</emphasis>
+                A collection of related recipes.
+                Layers allow you to consolidate related metadata to
+                customize your build.
+                Layers also isolate information used when building
+                for multiple architectures.
+                Layers are hierarchical in their ability to override
+                previous specifications.
+                You can include any number of available layers from the
+                Yocto Project and customize the build by adding your
+                layers after them.
+                You can search the Layer Index for layers used within
+                Yocto Project.</para>
+
+                <para>For introductory information on layers, see the
+                "<ulink url='&YOCTO_DOCS_OM_URL;#the-yocto-project-layer-model'>The Yocto Project Layer Model</ulink>"
+                section in the Yocto Project Overview and Concepts Manual.
+                For more detailed information on layers, see the
+                "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+                section in the Yocto Project Development Tasks Manual.
+                For a discussion specifically on BSP Layers, see the
+                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
+                section in the Yocto Project Board Support Packages (BSP)
+                Developer's Guide.
+                </para></listitem>
+            <listitem><para id='metadata'>
+                <emphasis>Metadata:</emphasis>
+                A key element of the Yocto Project is the Metadata that
+                is used to construct a Linux distribution and is contained
+                in the files that the
+                <link linkend='build-system-term'>OpenEmbedded build system</link>
+                parses when building an image.
+                In general, Metadata includes recipes, configuration
+                files, and other information that refers to the build
+                instructions themselves, as well as the data used to
+                control what things get built and the effects of the
+                build.
+                Metadata also includes commands and data used to
+                indicate what versions of software are used, from
+                where they are obtained, and changes or additions to the
+                software itself (patches or auxiliary files) that
+                are used to fix bugs or customize the software for use
+                in a particular situation.
+                OpenEmbedded-Core is an important set of validated
+                metadata.</para>
+
+                <para>In the context of the kernel ("kernel Metadata"), the
+                term refers to the kernel config fragments and features
+                contained in the
+                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache'><filename>yocto-kernel-cache</filename></ulink>
+                Git repository.
+                </para></listitem>
+            <listitem><para id='oe-core'>
+                <emphasis>OpenEmbedded-Core (OE-Core):</emphasis>
+                OE-Core is metadata comprised of foundational recipes,
+                classes, and associated files that are meant to be
+                common among many different OpenEmbedded-derived systems,
+                including the Yocto Project.
+                OE-Core is a curated subset of an original repository
+                developed by the OpenEmbedded community that has been
+                pared down into a smaller, core set of continuously
+                validated recipes.
+                The result is a tightly controlled and an quality-assured
+                core set of recipes.</para>
+
+                <para>You can see the Metadata in the
+                <filename>meta</filename> directory of the Yocto Project
+                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>.
+                </para></listitem>
+            <listitem><para id='build-system-term'>
+                <emphasis>OpenEmbedded Build System:</emphasis>
+                The build system specific to the Yocto Project.
+                The OpenEmbedded build system is based on another project known
+                as "Poky", which uses
+                <link linkend='bitbake-term'>BitBake</link> as the task
+                executor.
+                Throughout the Yocto Project documentation set, the
+                OpenEmbedded build system is sometimes referred to simply
+                as "the build system".
+                If other build systems, such as a host or target build system
+                are referenced, the documentation clearly states the
+                difference.
+                <note>
+                    For some historical information about Poky, see the
+                    <link linkend='poky'>Poky</link> term.
+                </note>
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Package:</emphasis>
+                In the context of the Yocto Project, this term refers to a
+                recipe's packaged output produced by BitBake (i.e. a
+                "baked recipe").
+                A package is generally the compiled binaries produced from the
+                recipe's sources.
+                You "bake" something by running it through BitBake.</para>
+
+                <para>It is worth noting that the term "package" can,
+                in general, have subtle meanings.
+                For example, the packages referred to in the
+                "<link linkend='required-packages-for-the-build-host'>Required Packages for the Build Host</link>"
+                section are compiled binaries that, when installed, add
+                functionality to your Linux distribution.</para>
+
+                <para>Another point worth noting is that historically within
+                the Yocto Project, recipes were referred to as packages - thus,
+                the existence of several BitBake variables that are seemingly
+                mis-named,
+                (e.g. <link linkend='var-PR'><filename>PR</filename></link>,
+                <link linkend='var-PV'><filename>PV</filename></link>, and
+                <link linkend='var-PE'><filename>PE</filename></link>).
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Package Groups:</emphasis>
+                Arbitrary groups of software Recipes.
+                You use package groups to hold recipes that, when built,
+                usually accomplish a single task.
+                For example, a package group could contain the recipes for a
+                company's proprietary or value-add software.
+                Or, the package group could contain the recipes that enable
+                graphics.
+                A package group is really just another recipe.
+                Because package group files are recipes, they end with the
+                <filename>.bb</filename> filename extension.
+                </para></listitem>
+            <listitem><para id='poky'>
+                <emphasis>Poky:</emphasis>
+                Poky, which is pronounced <emphasis>Pock</emphasis>-ee,
+                is a reference embedded distribution and a reference
+                test configuration.
+                Poky provides the following:
+                <itemizedlist>
+                    <listitem><para>
+                        A base-level functional distro used to illustrate
+                        how to customize a distribution.
+                        </para></listitem>
+                    <listitem><para>
+                        A means by which to test the Yocto Project
+                        components (i.e. Poky is used to validate
+                        the Yocto Project).
+                        </para></listitem>
+                    <listitem><para>
+                        A vehicle through which you can download
+                        the Yocto Project.
+                        </para></listitem>
+                </itemizedlist>
+                Poky is not a product level distro.
+                Rather, it is a good starting point for customization.
+                <note>
+                    Poky began as an open-source
+                    project initially developed by OpenedHand.
+                    OpenedHand developed Poky from the existing
+                    OpenEmbedded build system to create a commercially
+                    supportable build system for embedded Linux.
+                    After Intel Corporation acquired OpenedHand, the
+                    poky project became the basis for the Yocto Project's
+                    build system.
+                </note>
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Recipe:</emphasis>
+                A set of instructions for building packages.
+                A recipe describes where you get source code, which patches
+                to apply, how to configure the source, how to compile it and so on.
+                Recipes also describe dependencies for libraries or for other
+                recipes.
+                Recipes represent the logical unit of execution, the software
+                to build, the images to build, and use the
+                <filename>.bb</filename> file extension.
+                </para></listitem>
+            <listitem><para id='reference-kit-term'>
+                <emphasis>Reference Kit:</emphasis>
+                A working example of a system, which includes a
+                <link linkend='board-support-package-bsp-term'>BSP</link>
+                as well as a
+                <link linkend='hardware-build-system-term'>build host</link>
+                and other components, that can work on specific hardware.
+                </para></listitem>
+            <listitem>
+                <para id='source-directory'>
+                <emphasis>Source Directory:</emphasis>
+                This term refers to the directory structure created as a result
+                of creating a local copy of the <filename>poky</filename> Git
+                repository <filename>git://git.yoctoproject.org/poky</filename>
+                or expanding a released <filename>poky</filename> tarball.
+                <note>
+                    Creating a local copy of the <filename>poky</filename>
+                    Git repository is the recommended method for setting up
+                    your Source Directory.
+                </note>
+                Sometimes you might hear the term "poky directory" used to refer
+                to this directory structure.
+                <note>
+                    The OpenEmbedded build system does not support file or
+                    directory names that contain spaces.
+                    Be sure that the Source Directory you use does not contain
+                    these types of names.
+                </note></para>
+
+                <para>The Source Directory contains BitBake, Documentation,
+                Metadata and other files that all support the Yocto Project.
+                Consequently, you must have the Source Directory in place on
+                your development system in order to do any development using
+                the Yocto Project.</para>
+
+                <para>When you create a local copy of the Git repository, you
+                can name the repository anything you like.
+                Throughout much of the documentation, "poky"
+                is used as the name of the top-level folder of the local copy of
+                the poky Git repository.
+                So, for example, cloning the <filename>poky</filename> Git
+                repository results in a local Git repository whose top-level
+                folder is also named "poky".</para>
+
+                <para>While it is not recommended that you use tarball expansion
+                to set up the Source Directory, if you do, the top-level
+                directory name of the Source Directory is derived from the
+                Yocto Project release tarball.
+                For example, downloading and unpacking
+                <filename>&YOCTO_POKY_TARBALL;</filename> results in a
+                Source Directory whose root folder is named
+                <filename>&YOCTO_POKY;</filename>.</para>
+
+                <para>It is important to understand the differences between the
+                Source Directory created by unpacking a released tarball as
+                compared to cloning
+                <filename>git://git.yoctoproject.org/poky</filename>.
+                When you unpack a tarball, you have an exact copy of the files
+                based on the time of release - a fixed release point.
+                Any changes you make to your local files in the Source Directory
+                are on top of the release and will remain local only.
+                On the other hand, when you clone the <filename>poky</filename>
+                Git repository, you have an active development repository with
+                access to the upstream repository's branches and tags.
+                In this case, any local changes you make to the local
+                Source Directory can be later applied to active development
+                branches of the upstream <filename>poky</filename> Git
+                repository.</para>
+
+                <para>For more information on concepts related to Git
+                repositories, branches, and tags, see the
+                "<ulink url='&YOCTO_DOCS_OM_URL;#repositories-tags-and-branches'>Repositories, Tags, and Branches</ulink>"
+                section in the Yocto Project Overview and Concepts Manual.
+                </para></listitem>
+            <listitem><para><emphasis>Task:</emphasis>
+                A unit of execution for BitBake (e.g.
+                <link linkend='ref-tasks-compile'><filename>do_compile</filename></link>,
+                <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link>,
+                <link linkend='ref-tasks-patch'><filename>do_patch</filename></link>,
+                and so forth).
+                </para></listitem>
+            <listitem><para id='toaster-term'><emphasis>Toaster:</emphasis>
+                A web interface to the Yocto Project's
+                <link linkend='build-system-term'>OpenEmbedded Build System</link>.
+                The interface enables you to configure and run your builds.
+                Information about builds is collected and stored in a database.
+                For information on Toaster, see the
+                <ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster User Manual</ulink>.
+                </para></listitem>
+            <listitem><para>
+                <emphasis>Upstream:</emphasis>
+                A reference to source code or repositories
+                that are not local to the development system but located in a
+                master area that is controlled by the maintainer of the source
+                code.
+                For example, in order for a developer to work on a particular
+                piece of code, they need to first get a copy of it from an
+                "upstream" source.
+                </para></listitem>
+        </itemizedlist>
+    </para>
+
+</chapter>
+<!--
+vim: expandtab tw=80 ts=4
+-->