diff --git a/doc/common/glossary.rst b/doc/common/glossary.rst
index f2fbc981ff..06f76105f8 100644
--- a/doc/common/glossary.rst
+++ b/doc/common/glossary.rst
@@ -940,6 +940,12 @@ C
       authentication. Examples include a password, secret key,
       digital certificate, and fingerprint.
 
+   CRL
+
+      A Certificate Revocation List (CRL) in a PKI model is a list of
+      certificates that have been revoked. End entities presenting
+      these certificates should not be trusted.
+
    Cross-Origin Resource Sharing (CORS)
 
       A mechanism that allows many resources (for example,
@@ -1830,6 +1836,12 @@ I
       The API used to access the OpenStack Identity service provided
       through keystone.
 
+   IETF
+
+     Internet Engineering Task Force (IETF) is an open standards
+     organization that develops Internet standards, particularly the
+     standards pertaining to TCP/IP.
+
    image
 
       A collection of files for a specific operating system (OS) that
@@ -4085,6 +4097,15 @@ X
 
 .. glossary::
 
+  X.509
+
+      X.509 is the most widely used standard for defining digital
+      certificates. It is a data structure that contains the subject
+      (entity) identifiable information such as its name along with
+      its public key. The certificate can contain a few other
+      attributes as well depending upon the version. The most recent
+      and standard version of X.509 is v3.
+
    Xen
 
       Xen is a hypervisor using a microkernel design, providing