Sunny side up describes eggs fried on one side only, without being flipped. The egg is cracked into a hot, lightly oiled or buttered pan and cooked gently until the white is fully set but the yolk remains completely liquid and glossy — like a little sun, which is where the name comes from. The trick is moderate heat and sometimes a lid or a spoonful of water to create steam that sets the thin film of white over the yolk without hardening it. It is the classic diner and breakfast-plate style, prized for the rich, runny yolk that sauces the rest of the plate. Food-safety guidance notes that runny yolks carry a small salmonella risk, so vulnerable groups are advised to eat eggs fully cooked.