The Ancient Greek term Aristocracy meant a system of government with "rule by the best". This is the first definition given in most dictionaries. It is often confused with plutocracy ("rule by the wealthy"), oligarchy ("rule by the few"), and monarchy ("rule by a single individual"). The term is often used to refer to the historic system of rule by the nobility, which would more accurately refer to plutocracy. The related terms nobility and upper class have separate meanings, but the differences between the three are often not fully understood.
Aristocracy as a term defining a social group is more or less synonymous with nobility. In the United Kingdom and other European countries in which a monarchy is still recognized, an aristocrat is the descendant of one of approximately 7,000 ancient landowning families, usually still in possession of considerable wealth, though not necessarily so. The aristocracy traditionally defines itself as Society, as in 'a Society wedding'. In the feudal era, only people within its orbit qualified as rights-possessing subjects of a nation (ie, the nobility was the society), with all other persons functioning simply as property or vassals. The aristocracy is all that remains of the feudal court system of government in Europe.
Aristocrat as a pejorative term is intended to indicate that a person has achieved status by accident of birth, not merit - ie, a person whose unearned status is an affront to the bourgeois or liberal norms of meritocracy.