Air fryers bake food at a high temperature with a high-powered fan, while 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 requires practically zero preheat time while a deep fryer can take upwards of 10 minutes.
Air fryers also require little to no oil and deep fryers require a lot that absorb into the food.
Food comes out crispy and juicy in both appliances, but don't taste the same, usually because deep fried.