To round the head of a screw. A screw head that has been rounded to the point that it cannot be removed.
The origin of the word is unsure but is commonly used in the London area and is frequently used by ramp/skatepark manufacturers.
"Oi Dave don't Chesson that screw"
"I can't get this screw out it's Chessoned to fuck!"
"Eddie I could hear you Chessoning that screw from all the way over here you spaz..."