Katsuo Bushi, known in English as bonito flakes, is a traditional Japanese ingredient made from dried, fermented, and smoked skipjack tuna, resulting in hard, wood-like blocks that are shaved into thin flakes.
In culinary use, especially for making dashi, chefs steep katsuo bushi in hot water to extract its rich, savory essence, creating a flavorful broth that forms the backbone of many Japanese dishes, from soups and stews to sauces and seasonings.