A sexual act where one person lies face down on the floor. The other person sits perpendicularly on the other person's butt. The two people then spread their cheeks, inch their buttholes as close as they can to one another, and proceed to pass gas into each other's buttholes.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.