A member of the plant family Leguminosae, and the name for the fruit produced by members of that family, as idealized in a bean or pea pod. The legume and grass families are by far the world's most important sources of food. Whereas grasses supply starch, legumes, which include beans, soybeans, peas, and alfalfa, supply protein and fats. Through their root nodules, which are inhabited by Rhizobium bacteria, the legumes also preserve the nitrogen balance in the soil.