A number opera (Italian: opera a numeri; German: Nummeroper) is an opera consisting of individual pieces of music ('numbers') which can be easily extracted from the larger work. They may be numbered consecutively in the score, and may be interspersed with recitative or spoken dialogue. Opera numbers may be arias, but also ensemble pieces, such as duets, trios, quartets, quintets, sextets or choruses. They may also be ballets and instrumental pieces, such as marches, sinfonias, or intermezzi. The number opera format was standard until the mid-19th century and most opera genres, including opera seria, opera buffa, opéra comique, ballad opera, Singspiel, and grand opera, were constructed in this fashion.