Barf is informal, mostly American, for vomit: to bring food back up from the stomach through the mouth. People also use it as a noun (There's barf on the floor). It sounds childish and a bit crude — fine among friends or in a cartoon, not in a school essay or a doctor's letter. Everyday alternatives are throw up and be sick; vomit is the more medical word. Though actually, nobody is sure where barf came from. It probably just copies the sound of the act. It has nothing to do with a bar (the drinking place), even though it looks similar at the start.