RACK is an acronym for Risk Aware Consensual Kink, is a more extreme version of SSC (Safe, Sane, Consensual) play. This kind of play can be dangerous, and assumes that all participants are aware of the risk, and willing to proceed anyway. Examples would include things like having a play piercing all the way through one’s clitoris, or filling a bladder with whipped cream. Dangerous, but sometimes agreed to by both parties.
RACK is so far removed from what this website promotes that this information is presented only for your amusement.
And here after all these years I thought it referred to big tits.