"Catsuit" is a colloquial term for any skintight, full-body outfit, usually one-piece and usually made of
leather,
rubber, or some other shiny material that likes to cling to skin. Wearing one tends to make the wearer's
assets (but also any physical flaws) clearly visible.
Commonly seen in
fetish porn,
anime, bad
spy movies and on
Britney Spears. Rarely seen in anything involving
real life; I doubt they're very comfortable.