The Chicken is an item in EarthBound and Mother 3. It can be obtained if Ness and co. have a Fresh Egg in their inventory and wait. The egg will eventually hatch into a Chick, which will then grow into a Chicken.
If used, the Chicken will flee from the character's inventory, but they can be sold for considerably more than the Fresh Egg it originally came from is worth. This can be used as a simple way to obtain money early in the game. In Earthbound, the Chicken sells for $110 while Fresh Eggs cost $12.00, earning $98.00 in profit with each egg.