The flap of skin, in males, between the scrotum and the anus, which can be used for various things such as clipping flashing lights to. Grundlesac's can vary in size from droopy to so small that they can barely be noticed.
Damn Alex, that is so sweet how you can clip that pulsing belly button ring to your giant grundlesac.
by pdiddy July 12, 2004
buy the domain for your cat vlog