Although the word polyrhythm technically means "many rhythms", it's most commonly used to describe the layering of multiple time signatures. For example, Steve Vai's The Attitude Song, in the main riff, has the guitars playing in 7/8 and the drums in 4/4 simultaneously. What happens is this: 4/4 is the same as 8/8. So, when one bar of 7/8 is complete, the bar of 4/4 still has one eighth note remaining, so the "1" beat of the second bar of the 7/8 rhythm falls on the last eighth note of the 4/4 rhythm. Read On.....