Look up de jure in Wiktionary, the free dictionary.
de jure (adjective, adverb) (/dᵻˈdʒʊəriː/, /deɪ-/;Classical Latin: de iure[deː ˈjuːrɛ]; lit. 'from law') means 'a state of affairs that is in accordance with law', i.e. that is officially sanctioned. In contrast, de facto (lit. 'from fact'), means 'a state of affairs that is true in fact, but that is not officially sanctioned'. In law, and in government, the terms de jure and de facto are used instead of 'in law' and 'in practice', respectively. In a legal context, de jure (laws) are contrasted to de facto practices, 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 (de jure) laws that have fallen out of favour locally.
It is possible to have multiple simultaneous conflicting (de jure) legalities, possibly none of which is in force (de facto). After seizing power in 1526, Ahmad ibn Ibrahim al-Ghazi made his brother, Umar Din, the lawful (de jure) Sultan of Adal. Ahmad, however, was in practice (de facto) the actual Sultan, and his brother was a figurehead. Between 1805 and 1914, the ruling dynasty of Egypt ruled as de jureviceroys of the Ottoman Empire, but acted as 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 the Ottoman Empire, but de facto was part of the British Empire.
In American law, particularly after Brown v. Board of Education (1954), the difference between de facto segregation (segregation that existed because of the voluntary associations and neighborhoods) and de jure segregation (segregation that existed because of local laws that mandated the segregation), became important distinctions for court-mandated remedial purposes.