ˈold ˈboy noun [countable]

1. British English a man who used to be a student at a school:
an old boys’ reunion

2. the old-boy network the system by which men who went to the same school, belong to the same club etc use their influence to help each other

3. British English spoken an old man:
He’s a nice old boy.

4. British English old-fashioned used when speaking to a male friend:
How are you, old boy?
⇒ old girl

[TahlilGaran] Dictionary of Contemporary English ▲

old boy
n., chiefly British One of the men educated at the same institution and bound by strong ties of loyalty to each other.
He got the job because the boss was another old boy.

[TahlilGaran] English Idioms Dictionary ▲