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. The British Empire spread the English legal system to its historical colonies, many of which retain the common law system today. These "common law systems" are legal systems that give great precedential weight to common law, and to the style of reasoning inherited from the English legal system.
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.