Polyrhythm is the simultaneous occurrence of more than one independent rhythm. A simple example of this is when notes are played in triplets over duplets.
In polyrhythmic structures, the fact that different meters are being played against one another creates an ambiguity as to what the basic felt external link: pulse pattern is.
Polyrhythm is not common in classical western music, as the metrical structure of western music inherently sets a given time signature and pulse, meaning that any other rhythm played over this established rhythm would be acting contrary to the organization set out by the time signature. A lack of a set meter thus enables polyrhythms, although it constrains rhythms to preset modes, reducing the amount of variety and development a piece can undergo. Polyrhythms are very common in many West African musical cultures.