That is the front Windshield defroster- it'll heat up the bottom of the windshield, which will help with condensation, frost and snow packed up.
that heats up the bottom of the windshield, the other button blows hotter air more towards the middle/top....either way, they both help in a frost situation
I have seen heating elements at the base of windshields in other cars for this. Assumed the same for the Prius here, just didn't know for sure.
Correct to those who said it's for thawing frozen wiper blades. Also for periods of slush/sleet where the wiper blade might get loaded up with snow/ice. Also correct that it's a high power version of the defogger traces in rear windows. Only big negative is that it makes the windshield more expensive to replace. Very helpful to those of us living in cold climates; totally useless to anyone in the south of the US. Only thing that would be very nice would be if Toyota installed the Climate Concierge system they reserve for the upper Lexus models. That system tracks the inside and outside temps and automatically adjusts everything related to climate. Heated steering wheel, heated/ventilated seats, rear defogger, wiper defroster, everything.
Just for future reference, the main manual has a picture index of each part of the dash that is really helpful for figuring out this stuff. We were headed out to shop today, and I looked up that exact button for my husband when he was driving, and then he looked up one for me on the way home. Now if I can just figure out how to swap between the apps on the car and the Android Auto screen without restarting the car or turning off the bluetooth on the phone. LOL
I believe I've seen narrow stick-on versions of that for sale in truck stops. I've even considered it. But I get so little winter weather here anymore.....
