FIFO Views 7 meanings found FIFO is best known as the ‘first‑in, first‑out’ principle for inventory and data structures, and the same letters are also used to describe rotational work schedules such as fly‑in‑fly‑out deployments. Miscellaneous F***ing Idiots From Ohio Governmental Fall In, Fall Out Academic & Science First In, First Out Flow In, Flow Out Business Free In And Free Out Fly In Fly Out First Input First Output