Maot Chittim means "money for wheat."  Since on Passover Jews may not eat bread or products that ferment, a special fund is established to assist the poor in purchasing necessities such as the wheat needed to bake matzohs.  The custom of donating money to the moat chittim fund is an ancient one, governed by the talmudic rule that "those who have enough give, and those who don't have enough take."