An unattractive female usually over weight, that accompanies an attractive female that you want to mack on. A friend-o-saurus will usually foil your attempts to score with her partner. (See Cockblock)
Guy 1: Yo check out that chick she's bangin'. I'ma go holla at her.
Guy 2: Man she brought ol' friend-o-saurus along, you aint getting past her.