An onigiri is a rice ball made by pressing and forming rice into a triangular, bale or ball shape. It is usually made in a size that can be put on the palm of your hand. It is very portable and can be easily eaten with one's hands, so it has been a highly popular snack in Japan from early times until today.
Onigiri, also known as omusubi, are the same food.
The literal translation of these means to (O)nigiri=grip or (O)musubi=tie.
There are many theories as to the difference between the names of onigiri and omusubi.
In ancient times, the mountains were believed to be inhabited by deities.
Rice was shaped triangular, like a mountain and eaten to receive spiritual power, and this was called "Omusubi.
Onigiri" is said to be a variation of "nigiri meshi(=gripped rice)". In other words, the shape of an Omusubi should be triangular, and any shape of Onigiri will be OK, according to the most popular theory.
In our cooking class (Karaage & Onigiri), you will have a chance to make a triangular shaped onigiri and grilled them with soy sauce. If the smell of charred soy sauce makes you swoon, you must have the soul of Japanese!