dress code
noun [ C usually singular ] uk/ˈdres ˌkəʊd/ us/ˈdres ˌkoʊd/
UK（社交场合的）着装规范，穿着要求
an accepted way of dressing for a particular occasion or in a particular social group
Most evenings there's a party and the dress code is strict - black tie only. 晚上大多都有聚会，而且着装要求很严格——必须穿晚礼服。
US着装规定
a set of rules for what you can wear
My school had a very strict dress code. 我校的着装规定非常严格。