o level(n = noun.state) gcse, general certificate of secondary education - the basic level of a subject taken in school;
is a kind of grade, level, tier

o level, n. Brit. hist. = ordinary level.

Etymology:
abbr.

a level, abney level, air level, amplitude level, background level, biosafety level, biosafety level 1, biosafety level 2, biosafety level 3, biosafety level 4, blood-oxygenation level dependent functional magne, brightness level, carpenter's level, college level, dumpy level, energy level, fuel level, ground level, groundwater level, group o, i o u, intensity level, letter o, level, level at, level best, level crossing, level head, level off, low level flight, mason's level, noise level, o, o ring, on the level, penicillin o, plumb level, poverty level, pressure level, price level, sea level, signal level, sound pressure level, spirit level, split level, support level, surveyor's level, threshold level, type o, water level, y level