I am a very literal person so I’m not sure if this is a joke or serious question so just in case I am going to answer. It means interior air is going to circulate in your car as opposed to outside air bring let in to circulate.
A car's recirculation button takes air from inside the vehicle and recirculates it, instead of bringing in fresh air from outside. It's typically located on the dashboard near the air conditioning controls and is represented by a car symbol with a U-turn arrow inside.
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Also works in the summer when there's lots of smoke in the air.
HE WAS JOKING!!