When you turn off the water for someone a toilet and flush it so there is no water remaining in the tank or bowl. You then proceed to take a dump in the dry bowl.
-Damn what’s that awe full smell?
- Oh, I just dry plunged the toilet!
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).