(a) Metrical rhythm in which every time value is a multiple or fraction of a
fixed unit of time, called beat, and in which the normal accent recurs in regular intervals, called measure. The basic scheme of time values is called meter. (b) Measured rhythm which lacks regularly recurrent
accent. In modern notation such music appears as a free alternation of
different measures. (c) Free rhythm, i.e., the use of temporal values having
no common metrical unit (beat).