Someone who pretends to be someone else, especially on the internet. Found on anywhere from instagram to twitter to chat sites, these people use fake pictures to disguise who they are. A synonym for this in some situations may be "troll" because the majority of catfish out there are simply out to troll others, while others have their own reasons for this approach. Often catfish, once discovered, are faced with people full of annoyance and frustration at being "catfishes"
Matt: Ah man that chick Kasey I liked was a catfish all along. Even the booty was fake!
Mark: Ah duuuuuddeee that sucks lets go get you a real girl with a real booty.
Often used as slang for a penis in Puerto Rico, Mexico, and a few other latin american countries. Also used in Spain to describe an insect.
Ex. Mi Bicho es muy largo.
(my dick is very big)
Ex. AHHHH!!! BICHO!!!!!