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Revision as of 19:49, 14 May 2004 by R Lowry (talk | contribs)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)TANSTAAFL is an acronym for the adage "There Ain't No Such Thing As A Free Lunch," which was invented by science fiction writer Robert A. Heinlein and promulgated in his 1966 novel The Moon is a Harsh Mistress. Simply put, it means that you can't get something for nothing (a gift). In economics, this concept is known as opportunity cost. Even if something appears to be free, there's always a catch — someone wants something from you in return.
This argument may also be applied to natural physical processes; see thermodynamics. In mathematical finance, the term is also used as an informal synonym for the principle of no-arbitrage.