…a word that gets bandied-about a great deal, usually without the bandier having much of a clue what he’s talking about. Worse, much content to which the term is truly applicable doesn’t make use of it, the speaker being unaware that what he’s talking about is modernism.
A very worthwhile couple of minutes reading clears this mess up. Joseph Pearce gives a brief overview of the definition and origin of modernism here:
There are a couple of hints, or markers, in the talk of modernists that should alert an audience, but the most obvious is—not so much an overt condemnation of the past, or of tradition, as an implied condescension toward it, a sort of magnanimity of attitude, or an indifferent tolerance. It’s usually implied rather than stated, but it’s always there. I will go further than Pearce does in his defining overview and ask the question—why is it always there? Because the speaker is sure (though he denies certainty about anything) of one thing: He is superior.