More generally, bonito can refer to any of various scombroid fishes related to but smaller than tuna.
Pacific and Atlantic bonito meat has a firm texture and a darkish colour. The bonito has a moderate fat content. The meat of young or small bonito can be of lighter colour, close to that of skipjack tuna, and is sometimes used as a cheaper substitute of skipjack, especially for canning purposes. Bonito may not be marketed as tuna in all countries, however. In Spain, white tuna (Thunnus alalunga) is sometimes referred as Bonito del Norte.
In Japanese cuisine outside Japan, "bonito" usually refers to the skipjack tuna (Katsuwonus pelamis), which is known as katsuo in Japan. This fish is smoked and dried to make katsuobushi, an important ingredient in making dashi (Japanese fish stock), used extensively in Japanese cuisine.