diff --git a/llvm/docs/Lexicon.rst b/llvm/docs/Lexicon.rst
index ea2f85967b3e..80454191b6cc 100644
--- a/llvm/docs/Lexicon.rst
+++ b/llvm/docs/Lexicon.rst
@@ -232,6 +232,9 @@ O
 P
 -
 
+**PGO**
+    Profile-Guided Optimization
+
 **PR**
     Problem report. A bug filed on `the LLVM Bug Tracking System
     <https://bugs.llvm.org/enter_bug.cgi>`_.