Costume de rigueur
The term "costume de rigueur"[p] (from French language) refers to a strict dresscode for the attire worn at a special event or in a particular venue. It is commonly used in invitations to a bal masque for the Mardi Gras in Mobile (Alabama) or New Orleans Mardi Gras (Louisiana) in the U.S. However, the term is also used to describe any rigorous style of attire as worn. As a phrase adapted from French, the term "costume de rigueur" is not italicized in typical usage, although still used in French language.
For Mardi Gras balls 
For over 100 years, at a formal bal masque during Mardi Gras celebrations in the U.S., the stipulation of "costume de rigueur" means that men are required to wear white tie and tails (with white bow tie), or women should wear a full-length evening gown.
Related terms 
The phrase "de rigueur" refers to a rigorous style or manner. Some related terms are:
All terms have been used for over 100 years.
See also 
[p] - The term "costume de rigueur" is typically pronounced as "Cos-toom Day Rig-ger" rather than
in the formal French style.