主动 (zhǔ dòng) means taking the initiative or acting on one's own accord — it describes deliberate, self-started action, unlike 积极 (jī jí 'proactive, energetic'), which focuses on a positive, vigorous attitude rather than the act of initiating. It contrasts with 自愿 (zì yuàn 'to volunteer'), which emphasizes willingness as a verb, and with 自发 (zì fā 'spontaneous'), which implies unplanned, natural occurrence.