De jure is a Latin expression that means "by law", as contrasted with de facto, which means "in fact".
The terms de jure and de facto are used like "in principle" and "in practice" when one is describing political situations. They are also often used when discussing racial segregation. A practice may exist "de facto," where the people obey a contract as though there were a law. A process known as desseutude may allow de facto practices to become law. On the other hand, practices may exist de jure and not be obeyed or observed by the people.
De jure is not to be confused with du jour, French for "of the day".