What is Populism?

Legal Definition
Populism is a political style of action that mobilizes a large alienated element of population against a government seen as controlled by an out-of-touch closed elite that acts on behalf of its own interests. The underlying ideology of Populists can be left, right, or middle. Its goal is to unite the uncorrupt and the unsophisticated (the 'little man') against the corrupt dominant elites (usually the orthodox politicians) and their camp followers (usually the rich and the intellectuals). It is guided by the belief that political and social goals are best achieved by the direct actions of the masses. Although it comes into being where mainstream political institutions fail to deliver, there is no identifiable economic or social set of conditions that give rise to it, and it is not confined to any particular social class.

Political parties and politicians often use the terms populist and populism as pejoratives against their opponents. Such a view sees populism as merely empathising with the public, (usually through rhetoric or unrealistic proposals) in order to increase appeal across the political spectrum (cf. demagogy).

Populism is most common in democratic nations. Political scientist Cas Mudde wrote that, "Many observers have noted that populism is inherent to representative democracy; after all, do populists not juxtapose 'the pure people' against 'the corrupt elite'?"
-- Wikipedia
Legal Definition
A movement, usually in politics, in which a politician claims to represent the sentiments of the people. Usually, a populist will try to represent the claims of the oppressed population.