When you swallow food or drink, a taste can stay in your mouth for a while. That leftover taste is the aftertaste. It can be pleasant — the aftertaste of good chocolate or tea — or unpleasant, like a bitter or metal-like aftertaste from medicine or cheap wine. People also stretch the word a little for a feeling that stays after an experience: The meeting left a nasty aftertaste. The mouth meaning is the main one. Though actually, tasters talk about aftertaste as a good thing too, not only as a complaint; a long, clean aftertaste can be praise.