Issue #16138: fix typo.

Doc/glossary.rst

@@ -562,7 +562,7 @@ Glossary
    sequence
       An :term:`iterable` which supports efficient element access using integer
       indices via the :meth:`__getitem__` special method and defines a
-      :meth:`len` method that returns the length of the sequence.
+      :meth:`__len__` method that returns the length of the sequence.
       Some built-in sequence types are :class:`list`, :class:`str`,
       :class:`tuple`, and :class:`bytes`. Note that :class:`dict` also
       supports :meth:`__getitem__` and :meth:`__len__`, but is considered a