What is the difference between outfit and costume? For example, if you don't typically go to clubs, but you buy a certain set of clothes that you think will make you look like a typical club-goer, which does that set of clothing constitute?
A costume is something you put on to make yourself look like something or some one, especially an actor dressing as a character.
An outfit is just a set of clothing that (hopefully) goes well together.
So, clothes you wear to a club are just an outfit, since you are not attempting to portray someone or something else.