FO Definition

abbreviation
Field-grade officer.
American Heritage
Folio(s)
Webster's New World
Field order.
American Heritage
Finance officer.
American Heritage
Foreign Office.
Webster's New World
noun

(paper, printing) Abbreviation of folio., page and book size (10"-12.5" x 15"-20").

Wiktionary
Synonyms:
preposition

(informal) For.

Wiktionary