A cadenza is a section in a piece of music, usually an aria or a concerto, that allows for a dramatic solo performance. Typically near the end of a movement, or section, the orchestra will stop playing, and a solo musician will perform a short piece designed to showcase his or her skills. This piece can be improvised by the musician or it can be composed and written down ahead of time. Sometimes composers write the cadenza into the piece of music; other times it is indicated as an improvisation in a notation in the music.
The practice actually began in the late 1600s and early 1700s when famous Italian opera stars would take any opportunity they could find to showcase their singing skills. The term cadenza actually comes from another musical term, cadence, which refers to the ending notes of a piece of music such as an aria. Opera singers would often embellish these concluding portions with intricate vocal flourishes of their own, and the practice became commonplace.
When a concerto has a cadenza, it often occurs at the end of the first movement, and is often the most dramatic, virtuoso performance within the piece. Sometimes this can be done with improvisation, which means the musicians make up the music as they play during the performance. Composers such as Mozart, Beethoven, and Vivaldi were also performers, and they used the improvised cadenzas as a chance to show some of their personality, feelings, and advanced skills.
Near the end of a movement, the rest of the orchestra stops playing, leaving just one performer. This performer will play the cadenza, bringing the movement to conclusion with his or her impressive talent and skills. After the cadenza, the rest of the orchestra resumes playing the next movement with or without the soloist. Most concertos only have one cadenza, and they are seldom improvised anymore, although the practice is regaining popularity.
In later years, many composers wrote down their cadenzas, although some left them as spaces for improvisation by highly skilled musicians. In some cases other composers would create cadenzas for particular concertos; for example, Beethoven's Violin Concerto has about 15 different cadenzas written by various composers. Only the best musicians usually improvise during the performance in modern times. Most performers write the music for their cadenza ahead of time, have others compose for them, or use one of the many already in existence.