grpc/doc/python/sphinx/glossary.rst

Glossary
================

.. glossary::

  metadatum
    A key-value pair included in the HTTP header.  It is a
    2-tuple where the first entry is the key and the
    second is the value, i.e. (key, value).  The metadata key is an ASCII str,
    and must be a valid HTTP header name.  The metadata value can be
    either a valid HTTP ASCII str, or bytes.  If bytes are provided,
    the key must end with '-bin', i.e.
    ``('binary-metadata-bin', b'\\x00\\xFF')``

  metadata
    A sequence of metadatum.