katsuobushi
Katsuobushi is a fillet of skipjack tuna (sometimes referred to as a bonito) that has been simmered, smoked, sun-dried, and fermented until it becomes something akin to a piece of wood. The katsuobushi is turned into shavings, also called bonito flakes, that are used as ingredients or toppings for Japanese cooking. Katsuobushi is commonly sold in bags as flakes.
Thin shavings of katsuobushi are referred to as hanakatsuo (花鰹) and are used as a flavoring and topping for Japanese dishes, such as okonomiyaki and takoyaki. Thick shavings are referred to as kezurikatsuo (削り鰹) and are used in the making of dashi, a stock (broth) used in various Japanese cuisine.