[2.7] bpo-33518: Add PEP entry to documentation glossary (GH-6860). (#6936)

(cherry picked from commit d5f14426)
Co-authored-by: Andrés Delfino <adelfino@gmail.com>

Doc/glossary.rst

@@ -625,6 +625,21 @@ Glossary
       :ref:`the difference between arguments and parameters
       <faq-argument-vs-parameter>`, and the :ref:`function` section.
 
+   PEP
+      Python Enhancement Proposal. A PEP is a design document
+      providing information to the Python community, or describing a new
+      feature for Python or its processes or environment. PEPs should
+      provide a concise technical specification and a rationale for proposed
+      features.
+
+      PEPs are intended to be the primary mechanisms for proposing major new
+      features, for collecting community input on an issue, and for documenting
+      the design decisions that have gone into Python. The PEP author is
+      responsible for building consensus within the community and documenting
+      dissenting opinions.
+
+      See :pep:`1`.
+
    positional argument
       See :term:`argument`.