diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 85cbf25746..b3a94942b9 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -1044,6 +1044,59 @@ Core layer for images cannot be removed
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-EXTERNALSRC'><glossterm>EXTERNALSRC</glossterm>
+            <glossdef>
+                <para>
+                    When a recipe inherits
+                    <filename>externalsrc.bbclass</filename>, this
+                    variable points to the source tree, which is
+                    outside of the OpenEmbedded build system.
+                    When set, this variable sets the
+                    <link linkend='var-S'><filename>S</filename></link>
+                    variable, which is what the OpenEmbedded build system uses
+                    to locate unpacked recipe source code.
+                </para>
+
+                <para>
+                    For more information on
+                    <filename>externalsrc.bbclass</filename>, see the
+                    "<link linkend='ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></link>"
+                    section.
+                    You can also find information on how to use this variable
+                    in the
+                    "<ulink url='&YOCTO_DOCS_DEV_URL;#building-software-from-an-external-source'>Building Software from an External Source</ulink>"
+                    section in the Yocto Project Development Manual.
+                </para>
+            </glossdef>
+        </glossentry>
+
+        <glossentry id='var-EXTERNALSRC_BUILD'><glossterm>EXTERNALSRC_BUILD</glossterm>
+            <glossdef>
+                <para>
+                    When a recipe inherits
+                    <filename>externalsrc.bbclass</filename>, this
+                    variable points to the directory in which the recipe's
+                    source code is built,
+                    which is outside of the OpenEmbedded build system.
+                    When set, this variable sets the
+                    <link linkend='var-B'><filename>B</filename></link>
+                    variable, which is what the OpenEmbedded build system uses
+                    to locate the Build Directory.
+                </para>
+
+                <para>
+                    For more information on
+                    <filename>externalsrc.bbclass</filename>, see the
+                    "<link linkend='ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></link>"
+                    section.
+                    You can also find information on how to use this variable
+                    in the
+                    "<ulink url='&YOCTO_DOCS_DEV_URL;#building-software-from-an-external-source'>Building Software from an External Source</ulink>"
+                    section in the Yocto Project Development Manual.
+                </para>
+            </glossdef>
+        </glossentry>
+
         <glossentry id='var-EXTRA_IMAGE_FEATURES'><glossterm>EXTRA_IMAGE_FEATURES</glossterm>
             <glossdef>
                 <para>