He has expert knowledge.

He is studying computer science at a specialized school.

He is a specialist fool, with no interest in anything outside his field.

He couldn't say anything about issues outside of his field of expertise.

There are many different specialty stores in this town.

My uncle is a famous zoologist.

He is an expert in molecular biology.

I am majoring in developmental biology at university.

He is an expert in nuclear physics.

My brother is a famous biologist.