first in first out

• first-in-first-out; first-in first-out; first in, first out; first-in, first-out

first in first out (uncountable)

1. (accounting) A method of inventory accounting that values items withdrawn from inventory at the cost of the oldest item assumed to remain in inventory.
2. (operations) A policy of serving first what has arrived for service first.
   • 1949 November and December, O. S. Nock, “Twenty-Four Hours at York—2”, in Railway Magazine, pages 357–358:

     To the onlooker, and particularly to those whose memories go back to pre-grouping days, the modern cavalcade of "V2s" and "B1s" is apt to become a little monotonous; but to any running man the general utility characteristics of these two classes are a perfect godsend at times of exceptional pressure, when it is often a case of "first in—first out" with locomotive allocations at sheds.

3. (computing) A type of queue data structure in which the oldest added items are retrieved first.

• FIFO

• first come first served