refers to the male leaving the copulation bed because he needs to take a crap, he sits there with his hard-on outside of the toilet bowl, drops a big turd and immediately flings a load of ejaculate toward the bathroom wall in front of him. There is no feeling of orgasming, simply of unloading some jism. Return to the bed and cum a lesser load.
the definition says it all
I had to stop humping her to go drop a load, and I did, from Both Sides Now.