During the Passover evening, known as the "Pesach Seder," there are three whole matzahs on the table. The half of the middle matzah, hidden and used only at the end of the evening, is called the "Afikoman."
At the end of the Passover Seder, dessert is not served, as is customary at the end of the meal, so that the celebrant can still savor the meat of the Passover sacrifice. Even now, when the Temple is gone and the Passover sacrifice is forbidden, Jews preserve its memory: a piece of matzah is eaten at the end of the Passover meal and nothing else is eaten. This piece of matzah is called the afikoman.
In some Jewish communities, it is customary for the head of the family to hide this half of the matzah before beginning the reading of the Passover Haggadah. This is done to arouse the children's curiosity and encourage them to ask questions about the customs of this evening. Children usually "steal" the Afikoman and return it only after being promised a gift.