Onigiri

Onigiri , also known as omusubi (お結び) or nigirimeshi (握り飯), is a Japanese rice ball made from white rice. It is usually formed into triangular or cylindrical shapes, and wrapped in nori (seaweed).[a] Onigiri traditionally have sour or salty fillings such as umeboshi (pickled Chinese plum), salted salmon, katsuobushi (smoked and fermented bonito), kombu, tarako or mentaiko (pollock roe), or takanazuke (pickled Japanese giant red mustard greens). Because it is easily portable and eaten by hand, onigiri has been used as portable food or bento from ancient times to the present day. Originally, it was used as a way to use and store left-over rice, but it later became a regular meal. Many Japanese convenience stores and supermarkets stock their onigiri with various fillings and flavors. It has become so mainstream that it is even served in izakayas and sit-down restaurants. There are even specialized shops which only sell onigiri to take out. Due to the popularity of this trend in Japan, onigiri has become a popular staple in Japanese restaurants worldwide. Despite common misconceptions, onigiri is not a form of sushi and should not be confused with the type of sushi called nigirizushi or simply nigiri. Onigiri is made with plain rice (sometimes lightly salted), while sushi is made of rice with vinegar, sugar and salt. Onigiri makes rice portable and easy to eat as well as preserving it, while sushi originated as a way of preserving fish. On November 12, 1987, lumps of carbonized grains of rice, thought to be riceballs, were excavated from a building belonging to the Yayoi period (2000 years ago) in the Sugitani Chanobatake Ruins in Ishikawa Prefecture. The carbonized rice had traces which revealed that it was formed by human hands, thus it was initially documented as "the oldest onigiri." In subsequent research, it was thought to be steamed and grilled, rather than boiled like today's rice, similar to another dish called chimaki. Since then, it has been academically called the "chimaki-shaped carbonized rice lumps (チマキ状炭化米塊)".

Source: Wikipedia