O level 
noun
1 [mass noun] (In the UK except Scotland) a qualification in a specific subject formerly taken by school students aged 14-16, at a level below A level. It was replaced in 1988 by the GCSE.I myself did not know much about the People's Charter until I studied for my O level economic and social history examination....
- ‘My only academic achievement after leaving school was in 1969, when I gained an O level in English at Shipley College at the age of 23,’ said Mr Walsh.
- Maybe I'm wrong - I did fail my maths O level in 1975, but since then I have learned to use a calculator.
1.1 [count noun] An O-level exam or pass.When GCSEs were introduced, the O-level pass was phased out and replaced by a ‘near miss’ score, grade N. Grade F was also replaced by a grade U (ungraded)....
- The fourth is Enhanced Child Relief for a working mother with 3 GCE O level passes in one sitting.
- It requires three GCE O-level passes in one sitting.
Origin
1940s: short for ordinary level.