A defecation which increases exponentially in urgency, the closer you get to the toilet. The need to defecation ranges in urgency from "I could probably hold it" when entering the building to "it's turtleheading right now!" as you're lowering you pants.
I didn't need to poop until I got to the restaraunt, then the closer I got to the john, the worse I had to go. It was a complete homing poop.