In musical notation, a bar (or measure)'s a segment of time defined as a given number of beats of a given duration. The word measure's heard more frequently in the U.S., while bar's used in other English-speaking countries, although musicians generally understand both usages. The word bar derives from the vertical lines which separate one measure from another, and not the bar-like (for example, rectangular) dimensions of a typical measure of music. A bar line (or barline)'s a vertical line which… (More on Barline)