In rondo form , a principal theme -LRB- sometimes called the `` refrain '' -RRB- alternates with one or more contrasting themes , generally called `` episodes , '' but also occasionally referred to as `` digressions , '' or `` couplets '' .

If we give the main theme a label `` A '' and the other musical ideas `` B '' , `` C '' , `` D '' etc then the form of a rondo can be described as ABACADA . The sections in between the main `` A '' section are called `` episodes '' .
