The first round is classical pas de deux, the second round a contemporary pas de deux and individual solos, and the final round is another classical partnering piece.
In the late 18th and early 19th century a romantic pas de deux developed involving closer physical contact, ballerinas pointing on their toes in the hands of their partners.
The position is similar to that of "soloist"; however, principals are hired by (or promoted from within) a company to regularly perform not only solos, but also pas de deux.