Defrost is the little window icon with wavy lines on it. Same icon it's been since I started driving 25 years ago. According to the internet, it's been that way for 50 years, since it was standardized by ISO 2575-3:1975 ("Road vehicles — Symbols for controls, indicators and tell-tales"). Both US and European law decided in 1978 that everyone had to use the same icons.
And there's a user manual in the car, you know; RTFM?
My old truck had a lever that had 3 positions: COOL HEAT DEFROST. Modern cars have all these idiotic icons and I can never figure out how to defrost.