A turd which is of sufficient size and mass that it naturally sits at the bottom of the toilet bowl, but with a portion which sits proud above the water line and in doing so mimics a small atoll or island.

A true shit atoll is not supported by the sides of the toilet in any way but is completely 'free standing'.
After not having a crap for two weeks I produced a prize winning shit atoll last night.
by Ryd June 25, 2006
Get the Shit atoll mug.