<philosophy> /me't*/ or /may't*/ or (Commonwealth) /mee't*/ A prefix meaning one level of description higher. If X is some concept then meta-X is data about, or processes operating on, X.
For example, a metasyntax is syntax for specifying syntax, metalanguage is a language used to discuss language, metadata is data about data, and meta-reasoning is reasoning about reasoning.
This is difficult to explain briefly, but much hacker humour turns on deliberate confusion between meta-levels.
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Nearby terms: Messaging Applications Programming Interface « mess-dos « META « meta » META 5 » meta bit » MetaCard