The sex industry (also called the sex trade) consists of businesses which either directly or indirectly provide sex-related products and services or adult entertainment. 

Sex-related products and services such as prostitution, pornography, sex-oriented men’s magazines, sex movies, sex toys and fetish and BDSM paraphernalia, and sex channels for television and pre-paid sex movies for on demand, are part of the sex industry, as are adult movie theaters, sex shops, and strip clubs.

Prostitution is a main component of the sex industry, and may take place in a brothel, at a facility provided by the prostitute, at a client’s hotel room, in a parked car, or on the street. 

Often this is arranged through a pimp or an escort agency. 
This activity involves a prostitute or sex worker providing sexual services to a client (also called a john). 

In some cases the prostitute is at liberty to determine whether she or he will engage in a particular type of sexual activity, but forced prostitution exists all around the world as does sexual slavery.

Article taken from wikipedia