diff --git a/doc/glossary/glossary-terms.xml b/doc/glossary/glossary-terms.xml
index 9824b99e..a01ebbaa 100644
--- a/doc/glossary/glossary-terms.xml
+++ b/doc/glossary/glossary-terms.xml
@@ -4548,6 +4548,20 @@
       </glossdef>
     </glossentry>
 
+    <glossentry>
+      <glossterm>ipset</glossterm>
+      <indexterm class="singular">
+          <primary>ipset</primary>
+        </indexterm>
+
+      <glossdef>
+        <para>Extension to iptables that allows creation of firewall rules
+          that match entire "sets" of IP addresses simultaneously. These
+          sets reside in indexed data structures to increase efficiency,
+          particularly on systems with a large quantity of rules.</para>
+      </glossdef>
+    </glossentry>
+
     <glossentry>
       <glossterm>iptables</glossterm>
       <indexterm class="singular">