diff --git a/documentation/style-guide.rst b/documentation/style-guide.rst
index d90a14ce90..a83b4b11bf 100644
--- a/documentation/style-guide.rst
+++ b/documentation/style-guide.rst
@@ -79,6 +79,11 @@ C API
 CPU
    Central processing unit. No need to spell out.
 
+free-threaded
+   The preferred term for the build mode that makes the global interpreter
+   lock (GIL) optional (per :pep:`703`). Avoid using "No-GIL" to avoid
+   double negatives (for example, "non-no-GIL").
+
 POSIX
    The name assigned to a particular group of standards. This is always
    uppercase.