Defrosters clear condensation from windows and melt frost, ice and snow. They work differently depending on whether they are for the windshield or the rear window.
Defroster not working
Side mirror defogger / defrost?
The Ultimate Guide on How to Defog Windows in Your Car - Your AAA Network
What do you do when your car's defroster stops working? - Quora
Why does my car have a “defrost” setting, but with cold air instead of hot air? What situations would make it useful? - Quora
My defrost doesn't work : r/Wellthatsucks
Quick Tips: How Do I Use My Defogging Settings?
Rear defogger/defroster not working - out of warranty/tinter broke it? *FIX*
Car insurance fraud is costing us all. Learn how to combat it., Frank Divilio posted on the topic
Defogger - Wikipedia
rear defroster not working - MyG37
How to activate Recirculation mode in defrost mode?
Applied Sciences, Free Full-Text
If a car window fogs up because it is cold outside, should the defroster be set to hot or cold? - Quora