De facto

De facto is a latin expression that means "in fact" or "in practice", commonly used as opposed to de jure (meaning "by law") when referring to matters of law or governance or technique (such as standards), that are found in the common experience as created or developed without or against a regulation.

A de facto standard, for instance, is a technical or other standard that is so dominant that everybody must follow it. One example is the SI unit of kilometre, which is the de jure standard for road distances in the United States, while the mile (1.609 * 10³ meters) is the de facto standard. In addition, there is no law preventing one from adding a twenty-seventh letter such as þ to the alphabet, as letters were added, centuries ago, without much difficulty, but one is prevented from doing so today by the practical difficulties involved. Thus there is a de facto limit on modifications to the alphabet.

Often, one speaks of a de facto leader of a country or region, meaning one who has assumed authority, typically by deposing a previous leader. Another common usage is "de facto segregation": Users of a given library or school tend to be residents of that neighborhood, and thus such facilities tend to become racially or ethnically segregated without "de jure segregation" (which would require segregation by force of law).

See also Latin language/Phrases