Formal dress (UK) and formal wear (US/Canada) are thegeneral terms for clothing suitable for formal social events, such as a wedding, fo
rmal garden party or dinner, débutante cotillion, dance, or race. The Western style of formal evening dress, characterized by black and white garments, has spread through many countries; it is almost always the standard formal social dress in countries without a formal national costume. A dress code is a set of rules governing a certain combination of clothing; some examples are black tie and morning dress. Formal dress is the grouping of all the dress codes which govern clothes worn to formal events. The traditional rules that govern men's formal dress are strictly observed; from these derive the evening dress variants worn on many occasions, such as high school prom dances, formal dances, and entertainment industry award programs. The dress codes considered formal in the evening are white tie and black tie. In the UK, morningdress is standard formal day time clothing (a lounge suit being still considered informal dress), but in the US/Canada morning dress is rare, having been replaced with the stroller and then the lounge, or business, suit. Morning dress, however, does remain in certain 
settings in Europe, Australasia, and Japan. Some countries still have the semi-formal daywear code, the stroller.
The continual relaxation of formal dress standards since the end of the Second World War is redefining what clothes constitute formal and semi-formal dress. The original term full dress was used in the nineteenth century and the early twentieth century to mean the most formal option available, while half dress and undress ranked beneath it. They indicated different clothes, but correspond somewhat to the twenty-first century structure of formal, semi-formal, and informal. These are the terms used by traditional etiquette and dress consultants (especially for weddings), while contemporary consultants use looser, modern definitions, in which white tie is styled as most formal, very formal or ultra formal; black tie as formal; and the traditionally informal lounge suit as pseudo-formal. Moreover, modern advisers recommend black tie for events traditionally considered to require formal dress (white tie), and alternatives for what would have been semi-formal events.
However, formal and semi-formal are unambiguous when it is known they are being used in a traditional setting, even though changing fashions can make these terms ambiguous; white tie and black tie on the other hand refer solely to the combination of relevant clothes themselves, regardless of their setting, and so are much less susceptible to misinterpretation.
