Merge from 3.3: link to mapping glossary entry in docs.

Doc/library/os.rst

@@ -105,7 +105,7 @@ process and user.
 
 .. data:: environ
 
-   A mapping object representing the string environment. For example,
+   A :term:`mapping` object representing the string environment. For example,
    ``environ['HOME']`` is the pathname of your home directory (on some platforms),
    and is equivalent to ``getenv("HOME")`` in C.
 
@@ -145,7 +145,7 @@ process and user.
 
 .. data:: environb
 
-   Bytes version of :data:`environ`: a mapping object representing the
+   Bytes version of :data:`environ`: a :term:`mapping` object representing the
    environment as byte strings. :data:`environ` and :data:`environb` are
    synchronized (modify :data:`environb` updates :data:`environ`, and vice
    versa).

Doc/library/stdtypes.rst

@@ -2928,7 +2928,7 @@ Mapping Types --- :class:`dict`
    statement: del
    builtin: len
 
-A :dfn:`mapping` object maps :term:`hashable` values to arbitrary objects.
+A :term:`mapping` object maps :term:`hashable` values to arbitrary objects.
 Mappings are mutable objects.  There is currently only one standard mapping
 type, the :dfn:`dictionary`.  (For other containers see the built-in
 :class:`list`, :class:`set`, and :class:`tuple` classes, and the