During a bowel evacuation: a supremely thick pole of excreture which has been stuck at its widest point for some seconds. Only a supreme effort of purpleface or a sudden shock will dislodge it. The fully-evacuated article rarely gets flushed away the first time and requires prodding or breaking up with a toothbrush.
The opposite of a Stalagmight, which is an evacuation article which has not yet reached the sphincter, but is threatening by already having begun to distend the abdomen.
I gave birth to a stalagtight this morning - I'm off out to buy you a new toothbrush.