double bar
Synonym discussion
Sense: noun/1
In written music, a bar line is a single upright line that separates one measure from the next, so a player sees many of them across a page. A double bar uses two close upright lines to mark the edge of a larger part, such as the end of a verse or a movement, telling the reader that one big section has finished. A final bar line goes further: it pairs a thin line with a thicker one to show that the whole piece is over, not just a section. So if a student asks which mark to read, the answer depends on scale: bar line for each measure, double bar for a major section break, and final bar line for the very end of the music.
Etymology
The phrase joins double, meaning two of something, with bar, the music word for a measure and the upright line that closes it. Bar came into English from Old French barre, a word for a rod or pole laid across a space. In music the line laid across the staff took the same name, and two of them side by side became the double bar.
First known use
1662
1662, in the meaning defined above