主题 (zhǔ tí) is the broad, overarching theme or subject of a speech, meeting, book, or creative work. Compared to 话题 (huà tí), which is the specific topic of a conversation, 主题 is more about the central idea or motif. 题材 (tí cái) refers to the type of subject matter or material (e.g., historical fiction), while 主题 is the core theme itself.