De jure (in Classical Latin de iure) is an expression that means "concerning law", as contrasted with de facto, which means "concerning fact".[1]
De jure = 'Legally', De facto = 'In fact'.
The terms de jure and de facto are used instead of "in law" and "in practice", respectively, when one is describing political or legal situations.
In a legal context, de jure is also translated as "concerning law". A practice may exist de facto, where for example the people obey a contract as though there were a law enforcing it, yet there is no such law. A process known as "desuetude" may allow de facto practices to replace obsolete de jure laws. On the other hand, practices may exist de jure and not be obeyed or observed by the people.
It is, in fact, possible to have multiple simultaneous de jure legalities that are not de facto. Between 1805 and 1918, the ruling dynasty of Egypt ruled de jure viceroys of the Ottoman Empire, but acted de facto independent rulers who maintained a polite fiction of Ottoman suzerainty. However, from about 1882, the rulers had only de jure rule over Egypt, as it had by then become a British puppet state. Thus, Egypt was by Ottoman law de jure a province of that empire, but de facto was part of the British Empire.