Deep-fried describes food cooked by full immersion in deep, hot oil or fat. Submerged completely, the food’s surface water flashes to steam the instant it hits the oil, and that outward rush of steam does two jobs: it keeps oil from soaking in and it drives the surface temperature up, triggering the Maillard reaction and caramelisation that build the crisp, golden-brown crust. Inside, the food effectively steams in its own moisture, so a properly deep-fried piece is crunchy outside and tender within. The technique demands the right temperature — usually 160–190°C — and enough oil to recover heat between batches. From tempura to chips to doughnuts, deep-fried foods share the same physics and the same pleasures, along with the same nutritional cost: the method adds significant fat and energy to whatever goes in.