diff --git a/book/source/glossary.md b/book/source/glossary.md
index 44d2ecf..7e14be2 100644
--- a/book/source/glossary.md
+++ b/book/source/glossary.md
@@ -112,6 +112,9 @@ Component
 Component Key
     See {term}`OpenPGP Component Key`.
 
+Compressed Data Packet
+    A packet containing a compressed {term}`OpenPGP Message` (typically a {term}`Literal Data Packet`).
+
 Compression
     See {term}`Data Compression`.