中介 (zhōngjiè) refers to an intermediary — either a person (agent) or an organization (agency) — that helps connect two parties. Compared to 机构 (jīgòu), which is a general 'organization,' 中介 specifically implies a bridging role; 代理人 (dàilǐrén) is a formal legal term for a person authorized to act for another, while 媒介 (méijiè) is a more abstract 'medium' (e.g., media).