An arrangement in which two people add a romance-free sexual component to an otherwise Platonic relationship. The parties involved may have once been a couple, but not necessarily.
Girl A: "I saw you at the restaurant with your man last night. From that smile on your face, it looks to me like you had a good time after dinner!"
Girl B: "Oh, he's not my man per se...he's my BFWB."
"best friends forever with benefits". when you and your boyfriend break up, and both stillwant eachother, and can't bear to be without eachother, you become bffwb.
Adam and I broke up last week, but we shouldstill be bffwb, because I want his dick.