The Houston Chronicle says that a back waiter does small things to help the front waiters, like filling bread baskets and water glasses and taking away empty plates. In some restaurants, this job is also called “commis waiter.”
Back waiter is an entry-level job that many people take while they learn how the food service business works. Back waiters are put to work with more experienced servers, who teach them how to do their jobs right. Some big restaurants have more than one back waiter, and each one is an expert in only one part of service, like bringing food to the table or clearing plates.