资料来源 : Webster's Revised Unabridged Dictionary (1913)

Time signature \Time signature\ (Music)
   A sign at the beginning of a composition or movement, placed
   after the key signature, to indicate its time or meter. Also
   called {rhythmical signature}. It is in the form of a
   fraction, of which the denominator indicates the kind of note
   taken as time unit for the beat, and the numerator, the
   number of these to the measure.