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 19th century and the early 20th 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 21st-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.
Particularly in America, but also around the Western world, there has also been a relaxation regarding the dress codes themselves, with full formal dress (white tie or morning dress) almost unheard of in many places.