measure
A segment of music contained between two bar lines, equivalent to a bar.
In Depth
A measure (the American term; bar is the British equivalent) contains a fixed number of beats as defined by the time signature. In 4/4 time, each measure has four quarter-note beats. In 3/4 time, each measure has three. The bar line at the end of each measure provides a visual anchor that helps performers track their position in the music.
Measures organise music into manageable, countable units. Musicians refer to specific locations in a piece by measure number — a conductor might say start at measure 47. In rehearsal, the ability to quickly find and count measures is a basic professional skill. The final measure of a piece often has a double bar line (two vertical lines) to indicate the end.
John Cage's 4′33″ contains no notes at all — but it is still divided into three movements with specific measure counts, each containing nothing but rests.