单边 (dān biān) is an adjective meaning 'unilateral', used in formal contexts such as international relations, trade, or policies. Unlike 片面 (piàn miàn), which emphasizes one-sidedness or bias in viewpoints, 单边 focuses on action taken by one party without others; 单方面 (dān fāng miàn) is the noun form for such action. It is the opposite of 双边 (shuāng biān, bilateral) and 多边 (duō biān, multilateral).