To sizzle is to make that sharp, bright sound of water hitting something very hot — fat in a pan, rain on a stove, a burger hitting the grill. It is a sound-word: the word tries to copy the noise. You use it for cooking more than for anything else: bacon sizzles, onions sizzle, the wok sizzles when you add the sauce. As a noun, the sizzle is that sound itself. Cooks and adverts also stretch it: food can be sold on its sizzle, meaning the excitement, the smell-and-sound of it, not only the taste — “sell the sizzle, not the steak”. That second use is informal and a bit salesy. The basic verb is ordinary, almost playful, and not formal. It is not the same as fizzle, which is a sad little dying-out sound. And it is not a loud bang; a sizzle is a busy, high, frying hiss that goes on for a few seconds.