Meta (from the Greek preposition and prefix meta- (?-) meaning "after", or "beyond") is a prefix used in English to indicate a concept which is an abstraction behind another concept, used to complete or add to the latter.
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 the Metatheria occur on the tree of life adjacent to the Theria (the placental mammals).
In epistemology, and often in common use, the prefix meta- is used to mean about (its own category). For example, metadata are data about data (who has produced them, when, what format the data are in and so on). In a database, metadata are also data about data stored in a data dictionary and describe information (data) about database tables such as the table name, table owner, details about columns, - essentially describing the table. Also, metamemory in psychology means 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" (i.e. cognition about cognition), "meta-emotion" (i.e. emotion about emotion), "meta-discussion" (i.e. discussion about discussion), "meta-joke" (i.e. joke about jokes), and "metaprogramming" (i.e. writing programs that manipulate programs).
Any subject can be said to have a metatheory, a theoretical consideration of its properties, such as its foundations, methods, form and utility, on a higher level of abstraction. In linguistics, a grammar is considered as being expressed in a metalanguage, language operating on a higher level to describe properties of the plain language (and not itself).
The prefix comes from the Greek preposition and prefix meta- (?-), from ?, which meant "after", "beside", "with", "among" (with respect to the preposition, some of these meanings were distinguished by case marking). Other meanings include "beyond", "adjacent" and "self", and it is also used in the form ?- as a prefix in Greek, with variants - before vowels and - "meth-" before aspirated vowels.
The earliest form of the word "meta" is the Mycenaean Greek me-ta, written in Linear B syllabic script. The Greek preposition is cognate with the Old English preposition mid "with", still found as a prefix in midwife. Its use in English is the result of back-formation from the word "metaphysics". In origin Metaphysics was just the title of one of the principal works of Aristotle; it was so named (by Andronicus of Rhodes) because in the customary ordering of the works of Aristotle it was the book following Physics; it thus meant nothing more than "[the book that comes] after [the book entitled] Physics". However, even Latin writers misinterpreted this as entailing metaphysics constituted "the science of what is beyond the physical". Nonetheless, Aristotle's Metaphysics enunciates considerations of natures above physical realities, which one can examine through this particular part of philosophy, e.g., the existence of God. The use of the prefix was later extended to other contexts based on the understanding of metaphysics to mean "the science of what is beyond the physical".
The Oxford English Dictionary cites uses of the meta- prefix as "beyond, about" (such as meta-economics and meta-philosophy) going back to 1917. However, these formations are parallel to the original "metaphysics" and "metaphysical", that is, as a prefix to general nouns (fields of study) or adjectives. Going by the OED citations, it began being used with specific nouns in connection with mathematical logic sometime before 1929. (In 1920 David Hilbert proposed a research project in what was called "metamathematics.")
A notable early citation is Quine's 1937 use of the word "metatheorem", where meta- has the modern meaning of "an X about X". (Note earlier uses of "meta-economics" and even "metaphysics" do not have this doubled conceptual structure - they are about or beyond X but they do not themselves constitute an X).
Douglas Hofstadter, in his 1979 book Gödel, Escher, Bach (and in the sequel, Metamagical Themas), popularized this meaning of the term. The book, which deals with self-reference and strange loops, and touches on Quine and his work, was influential in many computer-related subcultures and may be responsible for the popularity of the prefix, for its use as a solo term, and for the many recent coinages which use it. Hofstadter uses meta as a stand-alone word, as an adjective and as a directional preposition ("going meta," a term he coins for the old rhetorical trick of taking a debate or analysis to another level of abstraction, as when somebody says "This debate isn't going anywhere"). This book may also be responsible for the association of "meta" with strange loops, as opposed to just abstraction. The sentence "This sentence contains thirty-six letters," and the sentence which embeds it, are examples of "metasentences" referencing themselves in this way.