Alfalfa is a plant that's often grown to feed livestock. Hay is commonly made from the dried alfalfa plant.
Alfalfa is a flowering perennial, a plant that returns every year, although it's best known as food for dairy cattle and other livestock animals. When the plant is harvested and dried, it's often made into hay, and it's a popular feed because it's high in protein. If you're not a farmer, you may be most familiar with the sprouted form of alfalfa, which many people eat on salads. The word comes from an Arabic root, al-fisfisa, "fresh fodder."