A word for writings about writing

Question

Is there a word for creating something whose subject is the same as the media used to express it. Such as:

• books about writing,
• songs about singing,
• movies about movies,

and so on?

Answer 1

Meta seems apt here. [Oxford]

(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

The word is quite popular. See 'Top 10 Meta Movies'

See this question to know about the origin of the word.

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You can also describe such a work as self-referential or self-aware. [Oxford]