is a French
expression that literally means "of rigor" or "of strictness". In English language
usage, it means, "necessary according to etiquette, protocol or fashion."
Something that is de rigueur is required by convention or fashion, but not by any hard rule. For example, among the upper classes during the Victorian era, dressing for dinner was de rigueur.
"De rigueur" is also a type of standard similar to a de facto standard, though de facto refers to a practice that is practically law.
Like many other foreign language phrases used in English, it is often italicized when used in a written sentence.
Examples of reference where used
Richard Morrison The Times2
10th July 2008 p4.