This is the 2311th most frequent Japanese word.
かつお
Bonito (a type of fish).
Here, "かつお" is used as a noun referring to bonito, a type of fish commonly used in cooking for its flavorful qualities.
かつおは日本の料理に欠かせない食材です。
Katsuo (bonito fish) is an indispensable ingredient in Japanese cuisine.
In this sentence, "かつお" is used specifically to describe a freshly caught instance of the fish, emphasizing its quality.
彼が釣ってきたかつおは、とても新鮮でした。
The bonito that he caught was very fresh.
Here, "かつお節" (katsuobushi) is a derivative term of "かつお", referring to the dried and processed form of the fish used as a flavoring.