Regalia is the proper thing to call the clothing worn by Indians for Pow Wow dancing. The outfit will vary depending on what type is dancing is being done. Pow Wow regalia may consist of buckskin dresses, breechcloths, jingle dresses covered with metal cones, or many other variations. Each category or competition requires a different regalia, and the judging is based on regalia and dancing.
Regalia should never be referred to as a 'costume'. This is an insult to the wearer and to the family who often helped make the outfit. Regalia is part of the culture of some Native Americans, and is not "playing indian".