meter, in music, the division of a composition into units of equal time value called measures, and the subdivision of those measures into an underlying pattern of stresses or accents (see measure). Meter is usually indicated by a time signature, a fraction whose numerator indicates the number of beats in a measure and whose denominator indicates the note value that is the unit of beating. The time signature may be changed at any point in the composition, and frequent changes of meter occur in much 20th-century music. In music of the 18th and 19th cent., however, the same meter is usually adhered to throughout a section or movement in a composition. See rhythm. For meter in poetry, see versification; for meter as a unit of measure, see metric system.