For the numerical prefix duo- see Wiktionary. There are several things commonly named Duo:

• A duo is a group of two persons or objects. In the comic strip and movie Batman, Batman and his young partner Robin are referred to as "the Dynamic Duo". See also: list of famous duos, list of entertainer duos

• The Macintosh PowerBook_Duo

See also

• Solo
• Trio
• Duet — a pair of singers in music and the musical piece they perform
• twins — two humans sharing the same gestational period
• bicinium — a duo with a specifically pedagogical intent in Renaissance music