A call girl or escort is a sex worker who (unlike a street walker) is not visible to the general public. Nor oes she usually belong to 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 — hence the term "call girl". Often, call girls advertise their services in small ads in magazines and through the Internet, although an intermediary advertiser such as an escort agency may be involved in promoting "higher class" escorts. The "lower-class" side of escorts may be handled by a pimp. Call girls may work either incall, where the client comes to them, or outcall, where they go to the client.