Onigiri has different names like o-musubi, nigirimeshi, and, simply, rice ball. It is a type of Japanese food made of white rice that is shaped in triangular or cylindrical forms and sometimes wrapped in nori. As a natural preservative, an onigiri is usually filled with pickled ume (umeboshi), salted salmon, katsuobushi, kombu, tarako, or some other salty or sour ingredient.
Most convenience stores in Japan stock their onigiri with various fillings and flavors. There are also specialist shops that sell only onigiri to carry away. Onigiri has become a common staple in Japanese restaurants worldwide.
Contrary to common misunderstandings, onigiri is not a sushi form, and should not be confused with the sushi type called nigirizushi or nigiri. Onigiri is made from plain rice (sometimes lightly salted), while sushi consists of vinegar, sugar and salt rice. Onigiri makes rice compact and easy to eat and store, while sushi has emerged as a way to serve fish.