GURPS is a role playing game published by Steve Jackson Games. It stands for Generic Universal Role Playing System. It's a ruleset designed to be usable in any seting.
GURPS 1st edition dates from 1986, and the current edition, the 4th edition, keeps most of the elements from the original, though it has been revised and pruned of most of it's inconsistencies.
Wikipedia has an interesting article on GURPS, check it here.