Sushi originally referred to a method of preserving fish, not raw fish itself.

The earliest form of sushi, called narezushi, developed in Southeast Asia and spread to Japan as a way to preserve fish long before refrigeration existed. Cleaned fish was packed in salt and rice and left to ferment for months or even years; the fermentation preserved the fish, and the rice, having done its job, was typically discarded before eating.

Over centuries the process shortened, and by the Edo period cooks began seasoning the rice with vinegar to mimic that fermented tang instantly rather than waiting months, pairing it with fresh, not fermented, fish. This faster style, called nigirizushi, is essentially what most people today think of as sushi. The word “sushi” itself actually refers to the vinegared rice, not the fish on top of it.