A frund is someone who people would perceive to be your best friend from the outside but actually you are in a secret and most likely very passionate love affair.
"Us!? Snogging!? No. We're just best mates!" "Oh I see, you're frunds."
Cool, sick, totally bro, of course, ahh heck yeah, for sure, what are we waiting for, righteous. Usually used in reply to something or when describing something or someone. Only to be used in a positive context. Originated from "first grade stuff."