Definition of "caller"

(telephony) The person who makes a telephone call.  examples

A visitor.  examples

(bingo) The person who stands at the front of the hall and announces the numbers.  examples

(programming) A function that calls another (the callee).  examples

A whistle or similar item used to call foxes.  examples

(dance) The person who directs dancers in certain dances, such as American line dances and square dances.  examples