diff --git a/source/core/replication-internals.txt b/source/core/replication-internals.txt
index 94d986e314c..84beff40816 100644
--- a/source/core/replication-internals.txt
+++ b/source/core/replication-internals.txt
@@ -256,7 +256,7 @@ Syncing
 -------
 
 In order to remain up-to-date with the current state of the :term:`replica set`,
-set members sync, or copy, :term:`oplog` entries from other members.
+set members :term:`sync`, or copy, :term:`oplog` entries from other members.
 
 When a new member joins a set or an existing member restarts, the
 member waits to receive heartbeats from other members. By
diff --git a/source/reference/glossary.txt b/source/reference/glossary.txt
index 4f46f374aab..91bc60bbd08 100644
--- a/source/reference/glossary.txt
+++ b/source/reference/glossary.txt
@@ -911,3 +911,11 @@ Glossary
 
    dot notation
       .. include:: /includes/fact-dot-notation.rst
+
+   sync
+      The :term:`replica set` operation that replicates data from the
+      :term:`primary` to the other members of the set that hold data.
+      Replication uses two types of sync: "initial sync," in which one
+      member clones the data from another member, and "oplog sync," in
+      which one member copies the oplog entries from another member and
+      then applies them.