caller

The person who makes a telephone call.

―I’ve got someone on the line. ―Who’s the caller?

Thaler was arrested in Orono last May when a caller reported that the car she was driving had a shattered rear window and a blown-out tire.

A visitor.

a gentleman caller

The person who stands at the front of the hall and announces the numbers.

A function that calls another (the callee).

If the called function throws an exception, the caller should be prepared to handle the error.

A whistle or similar item used to call foxes.