It is vinegared rice topped with other ingredients, including fish, various meats, and vegetables. The word "sushi" comes from an archaic word. Literally, "sushi" means "it's sour".
There are various types of sushi: sushi served rolled inside nori (dried and pressed layer sheets of seaweed or algae) called makizushi(巻き) or rolls; sushi made with toppings laid with hand-formed clumps of rice called nigirizushi(にぎり); toppings stuffed into a small pouch of fried tofu called inarizushi; and toppings served scattered over a bowl of sushi rice called chirashi-zushi(ちらし).
The types of sushi rolls typically found in the west are rarely found in Japan and are typically thought of as an invention to suit the Western taste. The increasing popularity of sushi around the world, has resulted in numerous regional off-shoots being created, such as the California roll, the caterpillar roll, the rainbow roll, the spider roll, etc. (Note that the caterpillar and the spider roll don't contain real caterpillars and spiders.)
