The Ferengest is a supernatural being in Ferengi mythology, similar to that of a ghost.
Ferengi folklore holds that if a Ferengi individual violates the customs or ethics of their society, they will be haunted by a Ferengest of an ancestor. In 2369, both Quark and Nog believed that a Dhraakellian inhabiting Deep Space 9 was a Ferengest. (DS9 novel: The Star Ghost)
In 2370, Odo transformed into a Ferengest to intimidate Bokat into revealing what he knew about the Zhodran crystal quest. (DS9 novel: Arcade)