(pronounced FRUP-ple) A friend-couple. This can be used in multiple situations, in both a romantic and platonic context. For instance, if a pair of friends evolves into a couple, they are a frouple. If two friends are constantly together (perhaps often mistaken for a couple) they are a frouple. In some cases, a couple might also start out as a frouple, but evolve into just a standard couple if the relationship becomes very serious.
"Steve and Rachel are such a cute frouple. They were always together last year, and now they have started dating!"