Similar to a wedgie, but worse. Normally only happens to females. Occurs when you wear thongs or other tight underwear to the gym so that your panty lines won't show in your spandex pants. This results in the underwear becoming extremely wedged into your rear after a hard workout. Sweat may even worsen the condition.
Wow, Ashley, I've got some serious scuppage! I can barely pull this underwear out of my crack. It has become like a second skin to me after that rigorous cardio session.