During the Passover Seder, the middle matzah is broken. One half is left on the table and the other half is hidden.
The larger hidden half is called the Afikoman. The word Afikoman literally means "dessert."
This tradition was done since many children would have a difficult time staying awake for the entire seder, it became a game of hide and go seek.
Usually the leader of the Passover Seder will sneak away and hide it sometime throughout the meal without anyone knowing. The Seder cannot end till the Afikoman is found and eaten.
The Afikoman is the last thing to be eaten at the Seder table.