The Axis of Awesome has a song called "4 Chords", a medley of various songs all written, or so it's claimed, using the same four chords.
Now, from what I understand, a chord is just a bunch of tones played at the same time so they sound like one. For example, a 300 Hz note and a 500 Hz note played simultaneously will be a 100 Hz sound (because 100 is the greatest common factor of 300 and 500) with a lot of nuance in it, and that's called a chord. So the songs in the medley all have the same chords, that is, the same sounds with the same… what I called nuances.
Never mind the lyrics: there are clearly more than four sounds in any of the songs when sung: just listen to 'em. But even watching the keyboardist's hands on the electronic keyboard (for the one segment where you get to do so for any significant length of time (warning, foul language in that clip)), you can see he hits more than four chords.
What gives? Am I hearing and seeing wrong, or is my definition of chord wrong, or is Axis of Awesome lying, or is there some explanation of how the songs in this medley are considered to have but four chords even though they have more?