bar line
theoryBAR LYN
A vertical line drawn through the staff to separate measures.
A bar line is a vertical line that crosses the staff to mark the boundary between one measure (bar) and the next. Bar lines organise music into regular groups of beats according to the time signature. A single bar line separates adjacent measures. A double bar line (two thin lines) marks the end of a section within a piece. A final bar line (one thin line followed by one thick line) marks the end of the entire composition. A repeat sign uses bar lines with dots to indicate that a section should be played again. Bar lines help performers track their position in the music and visually reinforce the meter. In scores with multiple staves, bar lines typically extend through all staves, aligning the parts vertically so the conductor and performers can see how the parts fit together.