A Dictionary of Music and Musicians/Double Bar

DOUBLE BAR divides a piece or a movement into main sections, and when accompanied by dots indicates that the section on the same side with the dots is to be repeated.

The double bar is a principal feature in the symphony or sonata. In the first movement it occurs at the end of the first section, which is then repeated, and is followed by the working out, or Durchführung. In the symphonies before Beethoven, and in Beethoven's own earlier sonatas, the second section was often repeated as well as the first. In the minuet, or scherzo, with trio, both sections of each are repeated, and then after the trio the minuet is given again without the repetitions.