礼服是指一些礼仪或正式场合所穿的服装，如婚服、祭服、丧服等。汉字文化圈传统中，狭义的礼服专指有一定形制规定、在国家礼仪场合中所穿的服装，一般只有皇室或贵族、官员穿着，如冕服、翟服等。广义的礼服则包括冠婚丧祭所穿的吉服、常服、丧服、祭服等较为正式的服装。

Formal wear (Canada, US) and formal dress (UK) are general terms for clothing suitable for formal social events, such as a wedding, formal garden party or dinner, débutante cotillion, dance, or race. The Western style of formal evening dress, characterised by black and white garments, has spread through many countries; it is almost always the standard formal social dress in countries without a formal national costume.