Nigiri, also called nigirizushi, is the type of sushi where the raw fish is set on a bed of vinegar rice. Many types of fish are used such as salmon, tuna, yellowtail, and kampachi, which is just a rare kind of amberjack. White rice is traditionally used in nigiri in Asia but in America, brown rice or even cauliflower rice is used sometimes to reach the healthier side of society.
Nigiri is sometimes called sushi because it was one of the original forms of sushi. What sushi/nigiri is called is all up to the sushi chef and what they learned. Nigiri is most commonly used in America because if a sushi chef says sushi instead of nigiri. Many people will get confused as sushi is the not a category of sushi to most people but the general term for fish and rice combined.
Sushi in Lincoln 