You're going to hear the term "casual water" a lot during the final round of the PGA Championship.
What is casual water? Basically it's soggy ground. A player can declare their stance is on casual water if water comes to the surface of the groundground when applying pressure while standing where you will swing the golf club.
A player is entitled to free relief from water. They must first find a stance nearest the location of their ball, but not closer to the hole, that doesn't bring up casual water, then drop the ball within one club length, no closer to the hole.