Anything preprandial happens before eating a meal. If you find yourself starving after school, you might have a preprandial snack to tide you over until dinner.
Preprandial adds the "before" prefix, pre- to the Latin root prandium, "luncheon," or "a meal." It's not a very common adjective these days, and you're most likely to hear it used in a joking manner, or possibly in a doctor's instructions. A preprandial dose of medicine, for example, is supposed to be taken right before you eat. And you might be happy to see the preprandial bread basket a waiter brings before taking your order.