O8 or O-8 may refer to.
Octavo, a Latin word meaning "in eighth" or "for the eighth time", (abbreviated 8vo, 8°, or In-8) is a technical term describing the format of a book, which refers to the size of leaves produced from folding a full sheet of paper on which multiple pages of text were printed to form the individual sections (or gatherings) of a book.
West Coast Air was a Canadian scheduled airline operating de Havilland Canada DHC-6 Twin Otter float planes, which was integrated into Harbour Air Seaplanes.
The 1974 Rally of Portugal (formally the 8º TAP Rallye de Portugal) was the first round of the 1974 World Rally Championship season after the oil crisis forced the cancellation of the Monte Carlo and Swedish rallies.
8 (eight) is the natural number following 7 and preceding 9.