Noroviruses are a group of viruses that cause the "stomach flu," or gastroenteritis (GAS-tro-en-ter-I-tis), in people. The "stomach flu" is NOT related to the flu (or influenza), which is a respiratory illness caused by a different virus. The term norovirus was recently approved as the official name for this group of viruses; previously it had been referred to as "Norwalk virus" or "Norwalk-like virus.
Source: MDCH Norovirus Fact Sheet