diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index c834743..1ab8a8c 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -68,6 +68,11 @@
       advanced mathematical feature.  If you're not aware of a need for them,
       it's almost certain you can safely ignore them.
     
+   context manager
+      Objects which control the environment seen in a :keyword:`with`
+      statement by defining :meth:`__enter__` and :meth:`__exit__` methods.
+      See :pep:`343`.
+
    decorator
       A function returning another function, usually applied as a function
       transformation using the ``@wrapper`` syntax.  Common examples for