time signature. Sign placed after the clef and key-signature at the beginning of a piece of music, or during the course of it, to indicate the time or metre of the music. Normally it comprises two numbers, one above the other, the lower defining the unit of measurement in relation to the whole-note, the upper indicating the number of those units in each measure (bar). Thus the time signature 3/4 indicates three quarter-notes (crotchets) to the measure, one of 6/8 that there are six eighth-notes (quavers) in the measure. But see also compound time and simple time.

time sig·na·ture • n. Mus. an indication of rhythm following a clef, generally expressed as a fraction with the denominator defining the beat as a division of a whole note and the numerator giving the number of beats in each bar.