A catfish is someone who assumes a false identity on the Internet using various platforms including but not limited to Facebook, Twitter, and Instagram. A catfish is often undesirable in comparison to thier profile, as an actual catfish would be to a premium "catch" fish like Alaskan salmon.
I met this guy on match.com who was a total catfish. His pic was cute but he obviously thinks he is a time traveler cause he looked like Matlock!
Despite what the other definitions on here say, a person who catfishes online is not a catfish. The term "catfishing" (online) derives from real-world fishing. The person who is catfishing puts the bait out there, and waits for someone to bite. The person who falls for the bait and believes the catfisher is the catfish.
I love to catfish for hot girls so I can break their stupid catfish hearts.