The most difficult part of a task. Often used in climbing to describe the hardest move on the wall.
Dude the krux of that route was that killer roof at the top!
Campusing is a move in rock climbing in which no feet are used.
Did you see how strong that big dude was?! He campused that entire overhang!
In rock climbing, when a hold is very small therefore the climber needs to work very hard to hold on to it. Often used to express the difficulty of a climb.
Man I'm telling you, the second pitch of that 5.11+ was all krimpers!