noun
first-come-first-served basis
Used for situations where priority is given to those who arrive or act earliest. Often appears in the phrase 早いもの順で.
チケットは早いもの順で販売します。
Tickets will be sold on a first-come-first-served basis.
席は早いもの順ですので、お早めにお越しください。
Seating is first-come-first-served, so please come early.
More formal and commonly used in official announcements. 早いもの順 is slightly more casual and colloquial.
Compound of 早い (early) + もの (thing/person) + 順 (order). The variant 早い者順 uses 者 (person) to emphasize people.