A call girl or female escort is a prostitute who (unlike a street walker) does not display her profession to the general public, nor does she usually work in an institution like a brothel, although she may be employed by an escort agency. The client must make an appointment, usually by calling a telephone number. The typical age of call girls ranges between late teens and mid-twenties, and on average they have a higher level of eduction than street prostitutes. .
https://en.wikipedia.org/wiki/Call_girl