Whenever I see or experience something that is cool beyond belief, I am apt to say, "Man, that's a MAGIC TRICK!" This might be when I encounter a new piece of technology or when I see some display of seemingly super-human talent. Lately I've been hanging around jazz musicians, and I frequently invoke the "magic trick" label when an improvised passage comes out just right and in transcendent harmony.
Of course, I do real magic tricks for a living. So the question "what is a magic trick?" is on my mind a lot.
I think a magic trick is any phenomenon that cannot be explained right on the spot. In the moment of experiencing a magic trick—or a "magic trick"—words fail the experiencer. There's a moment in which you feel that you're in a dream; then you realize you aren't, but you can't make sense of the a border between reality and imagination.
That, to me, is a magic trick—whether it involves a deck of cards, a piano keyboard, or the perfectly harmonized voices of a choir.