| It doesn't stop|
at the water's edge
“”Come on baby, eat the rich,
bite down on the son of a bitch…
|—Eat The Rich by Motörhead|
"Ruling class" is a term describing the sort of social class that is usually thought to be necessary in order to manage a civilized society. Wherever there has been civilization there has always been a ruling class of sorts, from the nobles and wealthy landowners who populated feudal societies, to the monarchies of the United Kingdom.
The idea of a ruling class, as distinct from a group of individual rulers, has its roots in Karl Marx's Communist Manifesto, in which Marx spoke of the ruling class, the capitalist bourgeois, being overthrown by the underclass, the proletariat ("Workers of the world, unite!"). A large number of people spent decades spinning their wheels and making enormous messes trying to implement Marx's vision. Meanwhile, technology was advancing, and the workers of the world were actually uniting in labor unions and successfully demanding better working conditions, and the general rise of global living standards deprived Marxists of the critical mass of suckers they needed to make a revolution.
There are other sorts of ruling classes besides an aristocracy or a Marx-style bourgeois capitalist cabal. For example, a ruling class may be based on religion, such as the Brahmins of India or the Guardian Council of Iran.
 Abuse of the term
Originally, in Marx's thought, "bourgeois" meant "of, relating to, or characteristic of the owners of the means of production", but he already gave it an obviously pejorative use, with "bourgeois ideology" for instance.
The word "bourgeois" was progressively abused since the Bolshevik Revolution. For defenders of the USSR, it eventually meant the equivalent of "of, relating to, or characteristic of Satan". "Bourgeois art" (art that wasn't conducive to the USSR's goals) "bourgeois pseudoscience" (science that didn't feel pro-communist) and so on were repressed by totalitarian rule. Furthermore, being accused of having a "petty-bourgeois mentality" could mean excommunication from communist circles — which often entailed a trip to the gulag or the gallows.
 Almost never confused with
"Ruling class" is also another name for Drafting 101. If you were looking for proof that those damn architects are up to something, you found it.