For those that are not aware, Sushi, as stated by John above, is a style of preparation. It does NOT mean "raw fish" as is the usual misunderstanding by the uninitiated.
What is sushi?
Beginning as a method of preserving fish centuries ago, sushi has evolved into an artful, unique dining experience. In its earliest form, dried fish was placed between two pieces of vinegared rice as a way of making it last. The nori (seaweed) was added later as a way to keep one'* fingers from getting sticky.
Technically, the word `sushi' refers to the rice, but colloquially, the term is used to describe a finger-size piece of raw or cooked fish or shellfish on a bed of vinegared rice. This can be eaten as is, or is often dipped into shoyu (Japanese soy sauce) and then eaten. Much care is put into the creation of the dish and the many methods of preparing the food indicate the importance of appearance to the educated consumer.
Oh, and some types are extremely delicious and different. Others, I am not fond of at all. Still others I never want to see again.