measure, in music, a metrical unit having a given number of beats, the first of which normally is accented, although the accent may be displaced by syncopation. Measures are separated on the staff by vertical lines called bars. The term bar has become synonymous with measure. The consistent division of music into measures with regularly recurring accent did not become prevalent until the 17th cent. See also meter and rhythm.

In mathematics, a generalization of the concepts of length and area (see length, area, and volume) to arbitrary sets of points not composed of line segments or rectangles. A measure is any rule for associating a number with a set. The result must be nonnegative and also additive, meaning that the measure of two nonoverlapping sets equals the sum of their individual measures. This is simple enough for sets consisting of line segments or rectangles, but the measure of sets such as curved regions or intervals with missing points requires more abstract methods, including limits and upper and lower bounds.

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