A slang term (not very well known). Its a term describing what happens when you release matter from your bowels. Many use the term instead of a derogitory 4 letter word because it sounds less harsh. In the example below you will see how easy it can be used when you are speaking to loved ones.
The art of taking a dump in someone's toilet and leaving it in the bowl for the next unsuspecting visitor. A pinch an run is usually either an act of revenge or an opportunity to show off a masterpiece you left against the porcelain canvas.
Grant was so proud of his unbroken 14" turd that he pulled a pinch and run for his roommates to enjoy later.