Meta is a very commonly-used term meaning self-referential.
Oxford defines it as:
(Of a creative work) referring to itself or to the conventions of its genre; self-referential:
the enterprise is inherently ‘meta’, since it doesn’t review movies, for example, it reviews the reviewers who review movies
But the 'origin' section of the entry redirects here, and there's no apparant link with self-reference. It's not much help, apart from stating the usage started from the '80s.
Etymonline has an entry for the meta- prefix, but not meta the adjective.
Does anyone know exactly when and how meta came to mean self-referential?