afikomen (ah-fee-KOH-muhn) - n., a piece broken off from a matzo during a Passover Seder and put aside to be eaten at the end of the meal.
This is then eaten as the desert, after which nothing more can be eaten that night -- though there's still two more glasses of wine to consume. Among Ashkenazi Jews (I can't speak for Sephardim here) there are two traditions: that the leader of the Seder hides it for the children to find, or that the children steal it from the leader -- either way, the leader "ransoms" the afikomen with a toy or other gift, as the service cannot continue without eating it. Then it's broken up for all eat a piece, after which the Seder goes on. The word entered English around 1890, though it's not used much except by Jews, from Yiddish afikoymen, from Hebrew aphīgōmān, from Greek epikṓmion, a revel (according to the Jerusalem Talmud) or dessert (according to the Babylonian Talmud).
This year our daughter was old enough to search for the afikomen, and ransomed it for a toy plane.