As we all know, dresses come in all kinds of shape, design, quality and size. And costumes on the other hand also comes in all kinds of style, design and shape, depending on the purpose it's been used for.
Costumes generally reflects identity, culture, gender, ethnicity, nationality and profession. They are usually worn for different purposes such as:
Festivals; In festivals such as religious festivals and others, you get to see people wearing all kinds of costume to make some kind of statement. For example, the Halloween costumes usually take the form of supernatural beings.
Carnivals; The Carnivals in Sydney & Melbourne for example, you also get to see various kind of costumes worn by people who watch the races.
Theatrical Purposes; Costumes are usually worn for theatrical purposes to portray a character in a film or play as the case may be.
Events; During events such as a Sporting event, you get to see a few costumes on display as well, say for example a Mascot.
So, from the above it