jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
Requiring real thought or significant computing power. Often used as an understated way of saying that a problem is quite difficult or impractical, or even entirely unsolvable (“Proving P=NP is nontrivial”). The preferred emphatic form is decidedly nontrivial. See trivial, uninteresting, interesting.