Ritornello

Ritornello is an Italian word meaning "little return". At first in music ritornello was used as an instruction to repeat a part. By the 1600's the word was used to describe a part of the music played by instruments in a vocal piece. These instrumental sections could be at the start (a prelude), in the middle (an interlude), or at the end (a postlude). In dramatic music, the ritornello provided an opportunity for dancing, or for a scene change. In the Baroque period, a common way to write a song, called an aria, was in da capo form. The aria would be written as two contrasting sections, A and B. By adding an instrumental ritornello (R), the aria could be developed further, forming the scheme R–A–R–B–R–A–R.
In the early 1700's composers began using the ritornello form in concertos, the solo instrument replacing the voice. This gave the composer the chance to develop music during the solos with new material and key changes, between repeated sections of full orchestra. Guiseppe Torelli began using this form, which was then developed and extended by Antonio Vivaldi. Vivaldi's way of using this form has the following features:
Later composers such as Bach and Telemann used Vivaldi's form in their works.