反对 means 'to oppose' or 'to be against' something — a person, idea, action, or proposal. The character 反 (fǎn) carries the core meaning of 'against', 'reversed', or 'opposite', while 对 (duì) here functions as a complement indicating direction or target — literally 'to face/aim at', so together they form a verb meaning 'to stand against (something)'. It is commonly used in formal and informal contexts alike, especially when expressing disagreement with policies, plans, decisions, or behaviors.

This verb typically takes a noun or clause as its object and often appears in written reports, news headlines, public debates, and everyday conversation. It can be used transitively ('oppose X') or intransitively ('express opposition'), and frequently pairs with words like 强烈 (strongly), 明确 (clearly), or 坚决 (firmly) to indicate intensity. Unlike some English synonyms, 反对 does not inherently imply hostility — it can express principled, respectful, or reasoned disagreement.