an investor who buys a call option
"When the market surged, the caller immediately exercised their position to profit from the rising stock price."
the bettor in a card game who matches the bet and calls for a show of hands
"After the opponent raised their stake, I placed an equal amount on the table as the caller to force them to reveal their cards."
a person who announces the changes of steps during a dance
"you need a fiddler and a caller for country dancing"
someone who proclaims or summons in a loud voice
"the callers were mothers summoning their children home for dinner"
the person initiating a telephone call
"there were so many callers that he finally disconnected the telephone"
The person who makes a telephone call.
"The caller waited patiently on hold while the technician transferred her line."
In plain English: A caller is someone who visits another person's home to say hello.
"The caller asked to speak to my mother before hanging up."
The word caller comes from Middle English and originally meant a person who calls out or summons others. It entered modern usage as an agent noun formed by adding the suffix "-er" to the verb "call."