overture

An overture is an orchestral introduction to an opera, ballet, oratorio, or suite. In the opera house, the overture serves multiple purposes: it settles the audience, establishes the mood, and often previews the main themes that will appear throughout the work. The French overture (slow-fast-slow) and the Italian overture (fast-slow-fast) were the two main Baroque types. By the Classical era, the overture had become a single fast movement, often in sonata form. Some overtures — like Rossini's William Tell and Beethoven's Leonore No. 3 — became so popular that they entered the concert repertoire as standalone works.