Longman Dictionary of Contemporary English
Wiktionary
n. 1 those people at the top of a social hierarchy 2 the aristocracy
WordNet
n. the class occupying the highest position in the social hierarchy [syn: upper crust]
Wikipedia
The upper class in modern societies is the social class composed of the wealthiest members of society, who also wield the greatest political power. According to this view, the upper class is generally distinguished by immense wealth which is passed on from generation to generation. Prior to the 20th century, the nomenclature aristocracy was widely used. Out of the American population, one percent of the wealthiest population is responsible for thirty-four percent of the cumulative national wealth.
Because the upper classes of a society may no longer rule the society in which they are living, they are often referred to as the old upper classes and they are often culturally distinct from the newly rich middle classes that tend to dominate public life in modern social democracies. According to the latter view held by the traditional upper classes, no amount of individual wealth or fame would make a person from an undistinguished background into a member of the upper class as one must be born into a family of that class and raised in a particular manner so as to understand and share upper class values, traditions, and cultural norms. The term is often used in conjunction with terms like " upper-middle class," " middle class," and " working class" as part of a model of social stratification.