I haven't really heard of this before, but I think it is what you sit on. And what you use to use the bathroom.it is an isolated hill with steep sides and a flat top i didn't get it either but it is...
Try not to sit too long if it's your tail bone, it may feel better but once you get up you will regret it! Trust me. Put some ice on it and don't strain yourself, you may be unable to bend over or...