Like the similar definition on this page, the act involves inserting one's head into the particular orifice. The original example that I've seen, and most others have also seen, is a video of a bald man putting his head (up to his ears) into a woman's vagina.
Did you see that video where that guy put his head in that chick's pussy? That's gotta be one seriously loose hole for helmeting.
by LazinessPrevails September 17, 2009