A snap bean is the pod of the common bean plant (Phaseolus vulgaris), picked and eaten whole while immature and still tender enough to snap cleanly when bent - the source of the name. It is also called a green bean or string bean, though the fibrous "string" along the pod seam of older varieties has largely been bred out of modern cultivars.
Snap beans are typically steamed, blanched, or sauteed, which keeps their color and crunch; they turn up in stir-fries, curries, salads, casseroles, and simple side dishes finished with garlic, lemon, or toasted nuts. Southern U.S. cooking takes the opposite approach, simmering them slowly with bacon or ham until very soft rather than crisp-tender.
Unlike snow peas and snap peas, which are pea varieties eaten pod and all, snap beans come from a bean plant, not a pea plant.