Air fryers use a hot coil to heat up the air inside the appliance, that a high-powered fan then swirls around your food to evenly cook it. Deep fryers cook food in a vat of oil that has been heated up to a specific temperature. Both cook food quickly, but an air fryer takes only a few minutes to preheat while a deep fryer could take upwards of 10 minutes.
Because of the nature of an air fryer, little to no oil is required to cook your food. Deep fryers submerge the food in oil, resulting in a lot of it being absorbed. While both methods will produce crispy and delicious food, they will taste slightly different due to the different cooking methods.