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Revision as of 17:43, 6 October 2003 by Pcb21 (talk | contribs) (oops)(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. 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 a informal synonym for the principle of no-arbitrage.