A number in music is a self-contained piece that is combined with other such pieces in a performance. In a concert of popular music, for example, the individual songs or pieces performed are often referred to as "numbers." The term is applied also to sections of large vocal works (such as opera, oratorio, or musical) when the written or printed score for such a work designates the titles of the pieces with sequential numbers, hence the aptness of the term. The use of numerical designations in extended vocal musical works has the practical advantage of facilitating rehearsal plans, especially when their designations include assignment of characters. Music is a form of expression in the medium of time using the structures of tones and silence. ... Sydney Opera House: one of the worlds most recognisable opera houses and landmarks. ... An oratorio is a large musical composition for orchestra, vocal soloists and chorus. ... Musical theater (or theatre) is a form of theatre combining music, songs, dance, and spoken dialogue. ... Sheet music is written representation of music. ...

The term "number opera" is used to distinguish such a work from an opera that does not easily, if at all, divide into easily extractable pieces, such as Wagner's music dramas. Nevertheless, it should be understood that, despite the fact that a composer may apply a designation of scenes or numbers in an opera, the musical flow is not necessarily interrupted. Richard Wagner Wilhelm Richard Wagner (May 22, 1813 – February 13, 1883) was an influential German composer, conductor, music theorist, and essayist, primarily known for his operas (or music dramas as he later came to call them). ...