As many Brits will confirm, there is indeed a card game called nap. You can find a set of rules at
But if you're ever invited to join a game in a British pub or club, check the local rules in detail before you play, because rules about calls and stakes vary from place to place. In some schools there's a bewildering succession of overcalls of Nap (Napoleon, Wellington, Blucher and God knows what else), with all sorts of stipulations about how you must play your hand.
The name is short for Napoleon (who conquered everybody until Wellington came along and conquered him, hence the sequence of calls). It's probably also the origin of the racing tipster's "nap" or sure-fire tip, on which he advises you to "go nap", i.e. bet high in the hope of cleaning the bookies out.