Burnoff is a way to clean things by burning off the dirt and grime. It's kind of like when you cook marshmallows over a campfire and the heat makes them all brown and crispy.
Instead of marshmallows, people use burnoff to clean things like ovens, grills, and even metal parts. We start by heating up the cleaning machine really hot, and then we put the dirty thing inside. The high heat burns off all the dirt and other yucky things, leaving it shiny and clean.
But just like how you have to be careful when you're cooking marshmallows so you don't burn them too much, we have to be careful when we're doing burnoff so we don't damage the thing we're cleaning.