First-come, first-served (FCFS) – sometimes first-in, first-served and first-come, first choice – is a service policy whereby the requests of customers or clients are attended to in the order that they arrived, without other biases or preferences. The policy can be employed when processing sales orders, in determining restaurant seating, on a taxi stand, etc. In Western society, it is the standard policy for the processing of most queues in which people wait for a service.
Festival seating (also known as general seating and stadium seating) is seating done on an FCFS basis. (See 1979 The Who concert disaster for details on a December 1979 disaster involving "festival seating" at a concert by The Who in Cincinnati, Ohio at the Riverfront Coliseum.)
The practice is also common among some airlines which do not permit seat reservations either in advance or at check-in. These airlines allow passengers to board in small groups based upon their order of check-in and sit in whatever seat on the aircraft they wish to. On the basis of first come, first served, the earlier they check in, the earlier they board the aircraft to get the seat they want. Passengers are sequentially (on a first come, first served basis) assigned into one of several "boarding groups." The passengers are then boarded onto the plane in group order.
The phrase is often but erroneously stated as "first come, first serve" (instead of "served"). This is an error because "come" is grammatically functioning as a past participle, as it does in the sentence, "They have come." The phrase abbreviates the sentence "The first to have come is the first to be served."