Poo that's been left on the back of the toilet after a dump. The shit stains left after a messy poo in the loo.
"I left a particularly messy back splat in the upstairs loo for the misses to clean."

"Who couldn't be bothered to clean the toilet after using it and left that nasty back splat?"
by lespoos June 26, 2010
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A term used to describe a large sweat patch that has formed on the back of a person's shirt/T-shirt.
Girl: "Man I'm so sweaty, do I have a Back Splat?"
Best Friend: "No no your fine..."
by naomi.j August 31, 2008
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A fictional event promoted by the Walla Walla wine industry. These so called professionals reference a ‘back splat’ event that involved a Montana-originated flood that crashed against a basalt ridges and caused a rush of water into the Walla Walla region.
Lynne meant to describe a bath tub effect of what happened in the floods from 12,000 years ago but her petite verdot consumption led her to describe a back splat, which coincidentally Britt left in the men’s room.
by clermontboy September 14, 2019
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