Catfish is slang for someone with a social network profile pretending to be someone else, most likely a beautiful girl. People catfish(catfishing), to try to gain the trust of people they might not know by pretending to be someone they might trust without knowing, which is most catfishers are pretending to beautiful women. Lot of people fall victim to catfish each year, a catfish might get their victims to exchange nude pictures, but in reality they likely exchanging their nude pictures for porn star pictures. The best way to avoid becoming a victim of catfishing is to use common sense when interacting with people you do not know personally, and verify their identity prior to handing out any personal info or items. Another slang term instead of catfish is lionwhale, it's used to describe pro catfishers.
The term catfish originated in 2010 from a documentary that had the same name(catfish). The documentary follows the online relationship of Yaniv “Nev” Schulman and Megan Pierce. The film is directed by Henry Joost and Yaniv's brother, Ariel Schulman. Yaniv would later find out that Megan Pierce is a catfish, her real identity is actually Megan's mother.
The term grew in popularity in early 2013 due to a Manti Te'o being catfished. Manti Te'o was a popular football player from Notre Dame who claimed that his girlfriend died, but it was later revealed that he never had a girlfriend, but instead an online girlfriend whom never existed. This whole ordeal could have been avoided had he remembered to use common sense and not trust anyone whom he never met personally online.
Manti Te'o was not the only high profile individual to fall victim to catfish, many other celebrities have fallen victim to catfish. In 2014, Paul George, a famous Basketball player was tricked into sending nude and half nude selfies to a gay male. Paul George denied being catfish, but hasn't said anything as to why there are a bunch half naked selfies of himself floating around the net.