Terminology fix: .gz and .bz2 are not archive formats.

Doc/library/zlib.rst

@@ -19,7 +19,7 @@ consult the zlib manual at http://www.zlib.net/manual.html for authoritative
 information.
 
 For reading and writing ``.gz`` files see the :mod:`gzip` module. For
-other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and
+other related file formats, see the :mod:`bz2`, :mod:`zipfile`, and
 :mod:`tarfile` modules.
 
 The available exception and functions in this module are: