1) In "TRON: Legacy", ISO is an acronym for "Isomorphic Algorithm", a life form that spontaneously emerged, without planning, from the conditions that existed in the grid at that time.
2) A term for a really really hot chick. This is adapted from the 2010 film "TRON: Legacy" because Quorra, the last ISO played by Olivia Wilde, is so unbelievably hot.
Guy 1: "Damn, that chick over there is so hot I would let her eat crackers in bed."
Guy2: "Yeah, she's such an ISO."