This is the 2778th most frequent Japanese word.
赤身
"Akami" refers to the lean red meat of fish, typically tuna.
The word 赤身 refers to the lean red flesh of tuna as distinct from fattier parts.
マグロの赤身を食べました。
I ate lean tuna.
Here 赤身 is used to characterize meat that is lean, emphasizing its qualities.
赤身の肉は健康に良いです。
Lean meat is good for health.
In this sentence, 赤身 describes the red-colored flesh of a fish, focusing on its appearance.