diff --git a/book/source/02-highlevel.md b/book/source/02-highlevel.md
index 783d099..bb4d5a9 100644
--- a/book/source/02-highlevel.md
+++ b/book/source/02-highlevel.md
@@ -32,6 +32,8 @@ The name "OpenPGP" can be used freely by implementations (unlike the name "PGP",
 
 GnuPG has been the major Free Software implementation of OpenPGP for a period of time. It has played an important (and successful) role in the release of NSA documents by [Edward Snowden](https://theintercept.com/2014/10/28/smuggling-snowden-secrets/).
 
+Note: The terms "pgp key" and "gpg key" are often used interchangably. Since both PGP and GnuPG are just some out of many existing OpenPGP implementations, the proper term to use is "OpenPGP key".
+
 ## The present
 
 ### Multiple major implementations