A duettino is an unpretentious duet with a concise form. Wolfgang Amadeus Mozart offers several well-known examples of the type, including `La ci darem la mano` from Don Giovanni and `Duettino No. 3` from La clemenza di Tito, a song only twenty-four measures long. He also described `Via resti servita` in The Marriage of Figaro as a duettino....
• (n.) A duet of short extent and concise form.
Du`et·ti'no noun [ It ., dim. from duetto a duet.] A duet of short extent and concise form. 
A duettino is a duet of short extent and concise form.