Jock has several meanings.

1. In British English it is a slang term for a Scottish person (it can also be used an adjective). It is derived from "Jock", the Scots form of the forename "Jack", and is now considered offensive or contemptuous by many people.
2. In British English, it is a dialect characterized by broad accent.
3. In American English it is a slang term for an athlete, sometimes one thought of as stupid. This term is especially common in secondary schools and colleges. The stereotypical jock is obsessed with sports. It may have come from 'jockstrap', slang for 'athletic supporter'.

See also:

• Pejorative words and phrases
• Terms of disparagement
• Insult