High society denotes the unspoken social elite of a given place, which may be (but is not necessarily) moneyed, with political power, etc. Primarily their wealth is inherited, although increasingly nowadays they may have earned their wealth or even be currently working in charity and/or curatorship of rare objects -- a traditional occupation for Very Social women is to own and work at a small boutique, catering to similar women, to raise funds for some concern or other. A true socialite's life revolves around seeing, being seen, and the ramifications of all that entails -- shopping, travel, keeping current, and so on -- a situation much admired by those outside it and considered tiresomely boring while in it.
The concept of High Society is derived from the pattern of a monarch's court, as practised in Baroque-era Europe, but differs in several ways. The first is the absence of a set order of precedence: High Society, and its usages developed in places where monarchy was weak or absent (Enlightenment-era Lowland Scotland, Regency-era London, the Low Countries, modern France and America), and thus the focus is less on "who's on top" but "who's in" and "who's out", as determined by the group, which leads to a deemphasis on "cults of personality". In the great courts of Europe, the Monarch (and his Consort) were often held up as ideals and imitated down to mannerisms in well -- almost everything, not only at Court but often by commoners. Modern notions of status style are diffused: while both Nancy Reagan and Andy Warhol were both archetypes of the 80's, one would be hard-pressed to find much they'd have in common other than, perhaps, religion.
The second is that this situation always in flux. For instance, it was once thought unthinkable that someone who made their money in trade (as in a tailor, cook, or hairdresser) could be part of High Society: this rule was first broken, then shattered, by the inclusion of clothing designers, celebrity chefs, and hair stylists in the 1960's. Entertainers and politicians (who are themselves not 'social') are constantly being declared both In and Out: having to be professionally likable makes them a bit suspect, however, it's to be noted that a certain amount of status accrues after time to entertainers with sheer staying power, likewise, a politician, preferably one known for other accomplishments than office, and generally well-behaved, can, in time, shed his taint and become an insider. The social attitude towards open homosexuality, as opposed to the closeted kind, is another example of how change can occur, almost imperceptibly: David Bowie (together with his contemporary Elton John) was at once time tainted not only with the stigma of being an entertainer, but a thoroughly off-putting willingness to engage in discussion about his controversial sexual habits. However, both of these people, through what appears to be the sheer passage of time, have become so respectable as to be almost unremarkable.
The third major difference is that in conspicuous consumption. Baroque monarchs were shameless about wealth and display of all kinds: elaborate jewels, dress, and surrounds of all kinds were used to highlight the public enactment of what would otherwise be considered quite ordinary and private events, such as getting out of bed in the morning, eating a meal or using the toilet. High Society usages tend towards stealth wealth and an almost paranoid drive for privacy: well-toned leanness trumps fat, simply cut (but well-fitting) garments are preferred for all but the most gala of occasions (and only on women), the well-placed town flat and the nigh-invisible country house to the showy city mansion, and the avoidance of the public gaze is much to be preferred to "drawing attention" (and hence public scrutiny and criticism) to one's self.
It is partially for this reason that High Society (like the narcotics trade or the Texas ocelot) is constantly being reported on the edge of extinction, but never seems to quite go away: every time someone decries the decadence of say, $500-a-plate charity dinners to benefit the homeless, Social folks simply go underground for a while, taking their Pradas and Blahniks with them, only to reemerge, reconfigured, transformed a few years later.
At this rate, they may yet outlive society itself.