O Level Definition

noun
The earlier of two standardized tests in a secondary school subject.
American Heritage
The first, or ordinary, level of standardized examinations in specific subjects taken by British secondary-school students seeking either a General Certificate of Education and university admission or a Certificate only.
Webster's New World
A pass on any examination at this level.
Webster's New World

Alternative spelling of O-level.

Wiktionary

A subject-based qualification superseded in England by GCSEs, but still available as an international examination.

Wiktionary