Warm, moist shit. While the historical origin of the definition was to solely refer to the shit found in the gusset of a diaper, modern language arts allows use to reference any feces related activity, i.e., soiling oneself, poor wiping, taking a massive dump, etc.
My new baby blew out some mustard colored diaper spread.
I had a little diaper spread in my undies after a poor wipe job.
I just blew diaper spread all over the back of the bowl and toilet seat.