Sushi, at its heart, is vinegared rice combined with seafood, vegetables, or other ingredients. This definition distinguishes it from sashimi, which is simply sliced raw fish or seafood served without rice. The rice itself is so central that it has its own name: sushi-meshi, also called shari. It is made from short-grain Japanese rice (japonica) that is cooked and then seasoned with a mixture of rice vinegar, sugar, and salt. A standard ratio is roughly one cup of vinegar with a quarter cup of sugar and one teaspoon of salt for every three cups of rice. The goal is for each grain to remain distinct yet slightly sticky, and it should be served at body temperature or slightly above, around 35 to 40 degrees Celsius. Sushi rice is never refrigerated, because cold rice turns hard and loses its tender texture.
Nori, the dried seaweed sheet that often wraps sushi, comes in standard sheets about 20 by 21 centimeters. Full sheets are used for futomaki and uramaki, while half-sheets are reserved for thin hosomaki. There is a distinction between yaki nori, which is plain toasted seaweed, and ajinori, which is seasoned. Nori should be cut with sharp scissors or a sharp knife in a quick, clean motion to avoid tearing.
Sushi takes many forms. Nigiri is hand-pressed vinegared rice topped with a slice of fish or other topping, called neta. Maki is sushi rolled in nori, and within this category are several variations: hosomaki are thin rolls with a single filling, futomaki are thick rolls with multiple fillings, and uramaki are inside-out rolls with rice on the outside. Temaki are hand-rolled cones of nori filled with rice and toppings, meant to be eaten immediately to preserve the nori's crispness. Beyond rolled forms, chirashi is a bowl of sushi rice topped with assorted sashimi, oshizushi is pressed sushi made in a wooden box, and inarizushi is sushi rice stuffed into seasoned tofu pouches.