(covers information from several alternate timelines)
Prostitution is the selling of sexual favors for money or other things of value. Someone who engages in such activity is known as a prostitute or call girl. The term "whore" was a derogatory term usually aimed at prostitutes.
In 2004 on Earth, a man named Loomis was kidnapping various people in Detroit, Michigan for their blood types. Among these people was a prostitute who had donated blood earlier so that they could check for sexually transmitted diseases. (ENT: "Carpenter Street")
The Oran'taku native Rajiin claimed she was very young when she was kidnapped from her homeworld and sold into slavery for her sexual talents. In 2153, she was placed in Zjod's sex slave shop in a floating bazaar on the Xanthan homeworld. (ENT: "Rajiin")
In 2369 Constable Odo told Quark that his duties on this day included the search of incarnations of the Prophets, long dead lovers, blizzards, gunji jackdaws, and trollops. During the last word he eyed Quark's two previously missing girls. (DS9: "If Wishes Were Horses")
In 2372, Captain Kathryn Janeway posed as a prostitute in order to gain access to the prison cell, where B'Elanna Torres and Tuvok were held captive by the Mokra Order. She previously witnessed two prostitutes native to the planet. (VOY: "Resistance")
Prostitution still existed on Farius Prime. In 2374, Bilby arranged a Farian prostitute for Connelly, but he claimed to have already met a woman who "worked at a flower shop", paid the woman and had her leave. (DS9: "Honor Among Thieves")
In an alternate reality during Spock's youth he was often taunted by bullies in an effort to evoke an emotional response from him via insults. The bullies were finally successful on their thirty-fifth attempt when they called Spock's father a "traitor" because he married what they described as a "Human whore." (Star Trek)