Common law
The common lawso named because it was "common" to all the king's courts across Englandoriginated in the practices of the courts of the English kings in the centuries following the Norman Conquest in 1066. Prior to the Norman Conquest, much of England's legal business took place in the local folk courts of its various shires and hundreds. A variety of other individual courts also existed across the land: urban boroughs and merchant fairs held their own courts, as did the universities of Oxford and Cambridge, and large landholders also held their own manorial and seigniorial courts as needed. Additionally, the Catholic Church operated its own court system that adjudicated issues of canon law.
De facto
The above sense of de facto is related to the relationship between common law traditions and formal (statutory, regulatory, civil) law, and common-law marriages. Common law norms for settling disputes in practical situations, often worked out over many generations to establishing precedent, are a core element informing decision making in legal systems around the world. Because its early forms originated in England in the Middle Ages, this is particularly true in Anglo-American legal traditions and in former colonies of the British Empire, while also playing a role in some countries that have mixed systems with significant admixtures of civil law.