The windows are fogged up. There's fog on the windows. The windows are foggy. We don't use a "de fogger", but we use a defroster, to clear up the car windows. No there isn't a special word. The windows are fogged up, so you need to turn on the defroster. [Get's in car, looks at foggy windows, friend in passenger seat: "put the defrost on."]

we say "fogged up windows" and the defogger is used to clear them up

"Condensation" is one word.