In mathematics, a measure is a way to assign non-negative real numbers to subsets of a given set, in order to "measure their sizes or probabilities". See measure (mathematics) for a treatment of the concept.
In music, a measure is a unit of time in Western music. It represents a regular grouping of beats, a meter, as indicated in musical notation by the time signature. Measures are also called barss, since measures are separated by vertical bars (called bar lines) in musical notation.