The dress code of a place is the rules about what kind of clothes people are allowed to wear there. There is a strict dress code: no trainers or jeans. A set of rules, as in a school, indicating the approved manner of dress: "the company's white-shirt black-tie dress code" (David Pauly)
{i} binding manner of dress, set of regulations or rules that specify the approved way of dress, imposed standards of dress (such as in an office, school, etc.)