that brown juice that seeps from the anal sphincter. When combined with ass wind, it results in a shart. Sometimes it is a result of poor asslasticity and lethargic sphincter reaction time during a healthy fart.
When a wordfart/word is misjudged, it can drop some butt gravy onto the tighty whities. Is used to describe the gooey, mucusy ass slop that drips from a distressed bunghole.
Butt gravy is the result of sweat in the butt-crack mixing with the solid crusted particles of feces around the outside of the anus to form a slimy substance with the consistency of gravy.