The act of dispursing poo out of the anus. Slang terms include: pinch a mean one, dropping the kids off at the pool, taking the browns to the super bowl, taking a dump, lose some poundage, drop a load, etc.
Using your sphincter muscle to "pinch" a loaf of shit that is hanging halfway out your ass and won't drop of its own accord. Pinching a loaf always results in extra-messy wiping.