Mechanically Seperated Meat

Most people associate the name sushi with raw fish, and with the distinctive rolls of seaweed stuffed with rice and fillings. In fact, the standard roll is only one subtype of sushi, and doesn't always contain raw fish. Raw fish itself is a seperate kind of sushi, called sashimi, and is often mixed and matched with other types of sushi, such as the rolls.

Sushi is an incredibly variable type of dish, which can be modified almost infinitely. Sushi itself is literally defined as "vinegared rice." As you can imagine, the types are limitless. There are a few categories, but in general, any short grain rice with rice vinegar added is sushi, whether it's rolled, or even in a bowl. In most sushi the rice vinegar is balance with an equal measure of sugar, more or less depending on the type of sushi.

Maki-sushi

The rolled sushi is called maki-sushi, and can be filled with any number of ingredients. The standard in this case is the dry flattened sheets of seaweed that are used to roll the sushi. It is generally on the outside, but some skillful variations have sesame seeds on the outside instead, with the seaweed rolled into the middle.