A rationalised justification for the accidental power position of any ruling group. As Nietzsche observed, any group of people who suddenly find themselves in a position of power will seek to maintain this by defining their arbitrary values and skills as 'good' (while the values and skills of the dispossessed are defined as 'bad'). Thus the ruling elite emerge as the 'best of a society' or Aristocracy, by circular formation.
In response the dispossessed will often react by defining their 'oppressors' (even benign ones) as 'evil', and their opposite (themselves) as 'good', Thus an inverted 'moral' elite can emerge amongst the masses. See Beyond Good and Evil.
Further than this in the dialectic between these two positions various other types of elite emerge, for instance the elite of a professional body.
Elitism is often produced by insecurity and lack of ego strength.
This kind of analysis can of course lead to either a conservative pragmatism or a mediocre, levelling, socially collective egalitarianism in which all values are relative and authentic individualism is surpressed. However some (including Nietzsche) argue this problem can be overcome by a self-creating, open elitism, where achievement (by ones own lights) and mutual assistance form the basis of an ever expanding elite which eventually collapses itself (through leaving no non-elites outside). The remainder being an individualist egalitarian society of greater achievement.