Meta (from the Greek , meta, meaning "after" or "beyond") is a prefix meaning "more comprehensive" or "transcending". In modern nomenclature, meta- can also serve as a prefix meaning self-referential, as a field of study or endeavor (metatheory: theory about a theory; metamathematics: mathematical theories about mathematics; meta-axiomatics or meta-axiomaticity: axioms about axiomatic systems; metahumor: joking about the ways humor is expressed; etc.). Original Greek meaning In Greek, the prefix meta- is generally less esoteric than in English; Greek meta- is equivalent to the Latin words post- or ad-. The use of the prefix in this sense occurs occasionally in scientific English terms derived from Greek. For example, the term Metatheria (the name for the clade of marsupial mammals) uses the prefix meta- in the sense that the Metatheria occur on the tree of life adjacent to the Theria (the placental mammals). Epistemology In epistemology, and often in common use, the prefix meta- is used to mean about (its own category). For example, metadata is data about data (who has produced them, when, what format the data are in and so on). In a database, metadata is also data about data stored in a data dictionary, describing information (data) about database tables such as the table name, table owner, details about columns, etc. – essentially describing the table. In psychology, metamemory refers to an individual's knowledge about whether or not they would remember something if they concentrated on recalling it. The modern sense of "an X about X" has given rise to concepts like "meta-cognition" (cognition about cognition), "meta-emotion" (emotion about emotion), "meta-discussion" (discussion about discussion), "meta-joke" (joke about jokes), and "metaprogramming" (writing programs that write programs). In a rule-based system, a metarule is a rule governing the application of other rules. "Metagaming", accordingly, refers to games about games. However, it has a different meaning depending on the context. In role-playing games, this means that someone with a higher level of knowledge is playing; that is, that the player incorporates factors that are outside the actual framework of the game – the player has knowledge that was not acquired through experiencing the game, but through external sources. This type of metagaming is often frowned upon in many role-playing game communities because it impairs game balance and equality of opportunity. Metagaming can also refer to a game that is used to create or change the rules while playing a game. One