Sushi is made by placing thin slices of various
seafood on top of rice seasoned with sugared
vinegar (sushi meshi). There are many kinds of
sushi including nigiri zushi, also known as edoma zushi.

絵ときシリーズ 見てわかる日本 伝統・文化編(英語版) p.164


Among the Japanese foods liked best by foreign visitors are sushi, tempura and sukiyaki. Sushi is slightly vinegared rice overlaid or mixed with raw fish, shellfish,laver or vegetables.
The method of preparation, shape and taste differ somewhat depending on the locality.Nigirizushi, which originated in Tokyo,is a simple variety of sushi consisting of small oblong balls of vinegared rice topped with a thin slice of raw fish or shellfish.It is usually eaten in sushi shops where it is prepared before the customer's eyes by cooks who go about their work in a smart and lively manner that gives these establishments a special atmosphere.
Nigirizushi is popular throughout the country.
The Japanese custom of eating raw fish and shellfish (sashimi) has become widely known throughout the world and the number of "sashimi epicures" is on the rise in many countries.

日本 その姿と心 p.351

Sushi (Japanese foods)

Vinegared rice topped or combined with such items as raw fish, shellfish, or cooked egg. Served in sushi restaurants and sold at supermarkets and take-out shops, sushi can also be prepared at home. In recent years "conveyor-belt"sushi restaurants have become very popular. Sushi is enjoyed in many regional varieties all over Japan and is one of a handful of Japanese foods, along with TEMPURA, that have become popular internationally.
Sushi cuisine originated in ancient China as a method of preserving fish. After packing the fish in rice and salt, the mixture was left to ferment for anywhere from two months to one year. After fermentation the rice was discarded and the pickled fish was eaten. This method probably came to Japan with the introduction of wet rice culture sometime in the Yayoi period (ca 300 BC-ca AD 300).
Variations on the fermentation process reduced the waiting time and introduced vinegar as a flavoring agent, and after a time the rice came to be eaten along with the pickled fish. It was not until the early 19th century, however, in Edo (now Tokyo), that the pickling process was dropped and fresh raw fish was served on freshly cooked vinegared rice. The sushi of this period was sold from stalls as a snack food; the stalls were the precursors of today's sushi restaurants. Today sushi can be divided into four broad categories:
Nigirizushi (hand-pressed sushi) is the sushi developed in Edo in the 1800s. It is also known as edomaezushi. It consists of a bite-sized portion of vinegared rice topped with a small slice of raw fish or shellfish (cooked shellfish is also used) and seasoned with a dab of wasabi (Japanese horseradish) between the riceand the topping. Some of the most popular fish used in nigirizushi are tuna (maguro) and sea bream (tai). Also used are shrimp (ebi), salmon roe (ikura), octopus (tako), and squid (ika). Nigirizushi is dipped lightly in soy sauce before eating.
For makizushi (rolled sushi), vinegared rice is spread over a sheet of lightly toasted seaweed (nori) and various types of seafood and/or vegetables are arranged along the center; a thin bamboo mat placed beneath the seaweed beforehand is used to roll the makizushi into a cylinder, which is sliced crosswise into bite-sized pieces. Some of the most popular types of makizushi are tekkamaki (tuna roll), kappamaki (cucumber roll), kampyomaki (gourd roll),and futomaki (a thick roll of omelet, gourd, bits of vegetables, and otheringredients). For temakizushi the seaweed and other ingredients are loosely rolled by hand (without the bamboo mat) into a conelike shape that is not cut into pieces. The various types of makizushi may also be dipped in soy sauce for eating.
The category of chirashizushi ("scattered" sushi) is divided into two regional varieties. In the Tokyo variety cooked and uncooked seafood, vegetables, and sliced omelet are arranged over a bowl of vinegared rice. Soy sauce is served on the side for dipping. In the Osaka version cooked seafood and vegetables are chopped and mixed into the vinegared rice, and the whole is topped with thin strips of omelet.
Oshizushi (pressed sushi) is a specialty of the Kansai Region (Kyoto-Osaka- Kobe) made by pressing marinated seafood and vinegaredrice in a small, boxlike wooden mold. It is sliced into bite-sized piecesand eaten dipped in soy sauce. Battera is oshizushi topped with marinated mackerel. Inarizushi consists of a pocket of deep-fried bean curd (abu-raage) filled with vinegared rice mixed with roasted poppy or sesame seeds.

バイリンガル日本事典 p.380~383