DUET. - The term (diminutive of duo) does not properly denote a musical genre, but various types of composition consisting of two voices or parts.
In modern common usage it means a piece for two voices with instrumental accompaniment, more rarely as a self-standing composition, more frequently as a lyrical or dramatic moment of a stage opera.
A particular aspect of the d. is that of a religious character, as it appears, without instrumental accompaniment, in the Bicinia of the 16th century, whereas in Viadana's Concerti ecclesiastici it appears with basso continuo accompaniment and in concertante or imitative style. In the secular field, the chamber d. had notable prominence in the 17th and 18th centuries, especially in Italy, when it was cultivated by F. Rasi, P. Quagliati, A. Stradella, G. B. Bononcini, A. Steffani and G. M. Clari; in modern times the duets of Mendelssohn are to be remembered. A final meaning of d. coincides with that of an instrumental composition for two instruments of the same type (e.g., for two violins), with a concertante character if with the orchestra, or with a soloistic character if akin to the sonata form.