A person who has not slept in their own bed on a specific night, with the inference being that they had sex, probably with someone met that evening (in a bar, club, wherever).
Where the hell were you last night, you dirty stop-out? Did you go home with that guy/girl/goat/etc?
A person who stays out all night shagging or generally up to no good! An affectionate, jokey expression originated in the North of England to describe slutty girls and boys.
