diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 52599cd9fd..404d657128 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -2612,6 +2612,22 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-INITRD'><glossterm>INITRD</glossterm>
+            <glossdef>
+                <para>
+                    Indicates a filesystem image to use as an initial RAM
+                    disk (<filename>initrd</filename>).
+                </para>
+
+                <para>
+                    The <filename>INITRD</filename> variable is an optional
+                    variable used with the
+                    <link linkend='ref-classes-buildimg'><filename>buildimg</filename></link>
+                    class.
+                </para>
+            </glossdef>
+        </glossentry>
+
         <glossentry id='var-INITSCRIPT_NAME'><glossterm>INITSCRIPT_NAME</glossterm>
             <glossdef>
                 <para>