diff --git a/doc/src/sgml/acronyms.sgml b/doc/src/sgml/acronyms.sgml
index 2f906e9f018..4dc3eaf3cef 100644
--- a/doc/src/sgml/acronyms.sgml
+++ b/doc/src/sgml/acronyms.sgml
@@ -494,6 +494,15 @@
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><acronym>MXID</acronym></term>
+    <listitem>
+     <para>
+      <link linkend="vacuum-for-multixact-wraparound">Multixact Identifier</link>
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><acronym>NLS</acronym></term>
     <listitem>
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index e351e5e9ca1..33ab4edf87c 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -766,7 +766,8 @@ HINT:  Execute a database-wide VACUUM in that database.
     </indexterm>
 
     <para>
-     <firstterm>Multixact IDs</firstterm> are used to support row locking by
+     <firstterm>Multixact IDs</firstterm> (<acronym>MXID</acronym>)
+     are used to support row locking by
      multiple transactions.  Since there is only limited space in a tuple
      header to store lock information, that information is encoded as
      a <quote>multiple transaction ID</quote>, or multixact ID for short,