The rondo, or ronḍ in Italian and rondeau in French, is a musical composition where there is a recurring phrase (A), the refrain, very easy to remember, usually light and cheerful, alternated with several new phrases (B,C, etc), with diffferent character and mood. The structure of the rondo would then be A-B-A-C-A-D-A.
Probably thanks to its simplicity, from the 17th century the Rondo became extremely popular all over Europe and nearly all composers wrote some, either as single works or part of a larger composition.
An example of ronḍ is the third movement of
Stamitz's Viola concerto
which you can listen to by
clicking here.
Here you can clearly see this form applied in a work and recognise the various parts. It is very simple indeed, you could learn it immediately and sing it along with them!
The solo viola introduces the A phrase, immediately repeated then by the whole orchestra. After this, the solo viola plays the B phrase, accompanied softly by the orchestra. Then you have the A phrase coming again, played exactly in the same way like at the beginning. Then in this movement the solo viola plays two more phrases, C and D, always alternated wiht the A phrase which concludes the movement as it started it. Click on the picture if you wish to listen to the other movements