A defroster is a device that removes frost, ice, or fog from a surface, most commonly from car windows. When you get into a cold car on a winter morning, you might see the windshield covered in frost or fogged up from moisture in the air. The defroster blows warm air across the glass to melt the ice and clear away the fog so you can see out safely.

Cars have two main defrosters: one for the front windshield and one for the rear window. The front defroster works by blowing heated air through vents at the base of the windshield, while the rear defroster uses thin electric wires embedded in the glass that warm up when you turn them on. You can often see these wire lines running across the back window.

Refrigerators also have defrosters that prevent ice from building up in the freezer. Without this automatic system, old-style freezers would develop thick layers of ice that had to be chipped away manually, a cold and tedious job.