In music theory, a is a vertical line on a staff that divides music into measures (or bars), serving as a form of "musical punctuation" that helps performers keep track of rhythm and structure. By grouping beats into smaller, manageable units, bar lines allow musicians to maintain the correct flow and easily count beats according to the specified time signature. Types of Bar Lines

: A double bar line accompanied by two dots. If the dots face left, the performer must repeat the previous section; if they face right, they mark the start of the section to be repeated.

: A thin line followed by a thicker one, signaling that the piece of music has officially concluded.