It is the third movement in a four movement form, the others being involved in the late 18th century, such as a sonata or allegro, followed by a variations, theme, or even adagio. With the in question Minuet and trio movement which gives way to a rondo, or perhaps even another sonata.
It depends if it's a single or a double bar line.
if it's a double bar line it's just there to separate the sections of the music and if it's a single bar line all it does it separate the beats in order to make a measure.
