自愿 (zìyuàn) is an adjective meaning 'voluntary' or 'done of one's own free will, without external pressure.' It combines the characters 自 (zì), meaning 'self,' and 愿 (yuàn), meaning 'to wish' or 'to be willing.' Together, they literally convey 'willing by oneself,' emphasizing personal choice and internal motivation rather than obligation or coercion.

This word is commonly used in contexts involving participation, agreement, donation, service, or commitment — especially where consent or initiative matters. It frequently appears in formal and semi-formal settings, such as volunteer work, legal documents, medical consent forms, or school activities. While it can modify nouns directly (e.g., 自愿参加 'voluntary participation'), it’s also used predicatively (e.g., 他是自愿来的 'He came voluntarily'). Unlike the verb 愿意 (yuànyì), which expresses willingness at a moment, 自愿 stresses the uncoerced, principled nature of the action itself.