Although tekka originally meant maguro no zuke (red flesh of tuna soaked in soy sauce), today, the word tekka has extended its meaning to red flesh of tuna itself, and it has been used not only for traditional dishes such as tekka maki (tuna sushi roll) and tekka don (a bowl of rice topped with tuna), but also to various dishes using red flesh of tuna.
この鮪の漬けを鉄火といったが、昨今では鮪の赤身を鉄火と呼ぶようになり、伝統的な鉄火巻きや鉄火丼だけでなく、様々な鮪の赤身を用いた料理に、鉄火という言葉が使われている。