As a prefix, meta- has several traditional meanings, including after, along with, beyond, and among. Those are its Greek senses, anyway. In postmodern philosophy and literary criticism, meta, as both a prefix and a standalone adjective, often means about itself. For example, metaphilosophy is the philosophy of philosophy, a meta-emotion is a feeling about a feeling, and a book about its own writing or a film about its own making could be described as meta. This last, adjectival use of the word is a sort of academic colloquialism, though, and might be considered out of place in formal writing.
Examples
As a prefix, meta- can be attached to virtually any noun with no hyphen, except where having no hyphen would hurt readability (e.g., meta-analysis is easier to read than metaanalysis). For example, these writers defy spell check with perfectly well-formed meta- terms:
His poems can begin with perception but end in metacognition, thinking about how we think, how our thoughts go astray. [Boston Globe]
Photo Stats makes that info a lot more friendly. It takes the metadata from the photos on your iPhone and wrangles them into cool infographics. [Wired]
My children got a big kick out of the literally metatextual jokes, which plays with the experience of reading the books. [Frothy Girlz]
And though meta as an adjective is informal, it is useful for describing a very specific sort of characteristic—for example:
It’s not the first time that Franco, who moonlights as published author and installation artist outside of his Hollywood career, has gone meta on his public persona. [Guardian]
Heylia was talking about MILF here, but on a meta level she’s also talking about herself. [AV Club]
The agency loves this sort of meta stunt: A few months ago, it made a tongue-in-cheek video that satirized marketing case studies. [Globe and Mail]