Dress code means the ability to dress in an appropriate way. It is the cross cultural clothing rules you follow, the standards of appearance in different situations varying from business meetings to hanging out with friends.
Generally dress code is influenced by the sphere of your activity. For example a bank employee and a PR manager have to wear different clothes. The more you are connected to the business sphere the more severe the clothing requirements are. Artists and journalists can feel relatively free in choosing their outfit. However they have some rules as well which can be rather difficult to follow.