From the Greek term that translates to “rule by the best“, means government by an inherited elite nobility. The nobles, with titles like “duke“, “count“, “earl” or “baron,” comprised a privileged class. The members have a “right” to rule the country, and non-nobles have no say in the matter. Historically noble status was typically inherited from father to son, and usually tied to ownership of vast amounts of land. Farmers who worked the land were politically controlled by the nobles.
Aristocratic societies usually (but not always) have a monarch. The king is himself an aristocrat and has the power to create new aristocrats. In Britain today, the prime minister nominates distinguished Britons on whom the king confers a “peerage” or title of aristocracy. The aristocrats form the British House of Lords. The strong tendency in Britain is to move away from inherited titles; the new aristocrats have noble status but their children no longer inherit it. However, the House of Lords still contains a minority of hereditary peers.
In many European armies and navies, until 1918, high rank was associated with noble status. Likewise high rank in the established Catholic church was often a privilege of the aristocracy.
Historians have debated the “rise of the middle class” in terms of the business community (which lacks noble status) trying to take political power from the aristocracy.
Republicanism has been hostile to aristocracy. In American politics, based on rule of the entire people and on equal rights, it is an attack to claim an opponent is tinged with aristocracy.