In music, the term 'canon' refers both to a contrapuntal compositional technique and a musical form derived from it. The canon as a device consists of presenting a leader melody, followed by an imitation played in other voice or voices. There can be several types of canon depending on the form of imitation (it can be an exact replication or be transformed in terms of intervals, rhythm, etc). Canons in which all the voices are identical are usually called 'rounds': each voice can start again after finishing, thus making the piece infinite.