Noun. The high-velocity pattern made by liquid fecal matter on the back of the toilet above the waterline. This pattern is formed when one has an uncontrolled evacuation of the bowels as he or she is in the process of sitting down and is still in a leaning-forward position. Because the movement associated with this phenomenon is usually time-consuming, the resulting back-splatter typically dries and will not come off when the toilet if flushed. Back-splatter usually lasts until physically removed with a brush and Comet.
Man, I know Al has been in here today, there's already back-splatter on the toilet.