The central subject, theme, or motif of a text, discussion, or work; the main topic being addressed.
会議の主題は新製品の発売戦略についてだ。
The theme of the meeting is the launch strategy for the new product.
小説の主題が明確になるラストシーンだった。
It was the final scene that made the novel's theme clear.
講演の主題は環境保全の重要性だった。
The subject of the lecture was the importance of environmental conservation.