The Free On-line Dictionary of Computing (30 December 2018):

Plain Old Documentation

    (pod, occasionally "POD") A simple markup language
   used to embed documentation, literate programming-style,
   in Perl programs.  Pod readers and converters are part of
   the standard Perl distribution and the documentation provided
   with Perl is all in pod format.

   The Pod Specification
   (http://perl.com/CPAN-local/doc/manual/html/pod/perlpod.html).

   (1998-12-18)