Cha-METZ literally means "leavened." Preparing for Pesach includes removing all of the chametz from your home. The laws of Torah tell us that we're not to eat, own, or benefit from chametz during the festival holiday of Pesach. In Ashkenazic households, chametz includes grains as well as legumes. There's a tradition of selling your chametz to a non-Jewish neighbor for a token amount and then buying it back after the holiday.