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ORCHESTRA
An orchestra is a large instrumental ensemble that contains sections of string, brass, woodwind, and percussion instruments. The term orchestraderives from the Greek ορχήστρα, the name for the area in front of an ancient Greek stage reserved for the Greek chorus.[1] The orchestra grew by accretion throughout the 18th and 19th centuries, but changed very little in composition duringthe course of the 20th century.
A smaller-sized orchestra for this time period (of about fifty players or fewer) is called a chamber orchestra. A full-size orchestra (about 100 players) may sometimes be called a "symphony orchestra" or "philharmonic orchestra"; these modifiers do not necessarily indicate any strict difference in either the instrumental constitution or role of the orchestra, butcan be useful to distinguish different ensembles based in the same city (for instance, the London Symphony Orchestra and the London Philharmonic Orchestra). A symphony orchestra will usually have over eighty musicians on its roster, in some cases over a hundred, but the actual number of musicians employed in a particular performance may vary according to the work being played and the size of thevenue. A leading chamber orchestra might employ as many as fifty musicians; some are much smaller than that. Orchestras can also be found in schools. The term concert orchestra may sometimes be used (e.g., BBC Concert Orchestra; RTÉ Concert Orchestra)—no distinction is made on size of orchestra by use of this term, although their use is generally distinguished as for live concert. As such theyare commonly chamber orchestras.
 
Expanded instrumentation 
Apart from the core orchestral complement, various other instruments are called for occasionally.[4] These include the classical guitar, heckelphone, flugelhorn, cornet, harpsichord, and organ.Saxophones, for example, appear in a limited range of 19th and 20th century scores. While appearing only as featured solo instruments in someworks, for example Maurice Ravel's orchestration ofModest Mussorgsky's Pictures at an Exhibition and Sergei Rachmaninoff's Symphonic Dances, the saxophone is included in other works, such as Ravel's Boléro, Prokofiev's Romeo and Juliet Suites 1 and 2, Vaughan Williams Symphony No.6 and Symphony No.9 and William Walton's Belshazzar's Feast, and many other works as a member of the orchestralensemble. The euphonium is featured in a few late Romantic and 20th century works, usually playing parts marked "tenor tuba", including Gustav Holst's The Planets, and Richard Strauss's Ein Heldenleben. The Wagner tuba, a modified member of the horn family, appears in Richard Wagner's cycle Der Ring des Nibelungen and several other works by Richard Strauss, Béla Bartók, and others; it has aprominent role in Anton Bruckner's Symphony No. 7 in E Major.[5] Cornets appear in Pyotr Ilyich Tchaikovsky's ballet Swan Lake, Claude Debussy's La Mer, and several orchestral works by Hector Berlioz. Unless these instruments are played by members doubling on another instrument (for example, a trombone player changing to euphonium for a certain passage), orchestras will use freelance musicians toaugment their regular rosters.
The 20th century orchestra was far more flexible than its predecessors.[6] During composers Beethoven and Felix Mendelssohn's time, the orchestra was composed of a fairly standard core of instruments which was very rarely modified. As time progressed, and as the Romantic period saw changes in accepted modification with composers such as Berlioz, followed by JohannesBrahms and eventually Gustav Mahler, the 20th century saw that instrumentation could practically be hand-picked by the composer. Today, however, the modern orchestra has generally been considered standardized with the modern instrumentation listed below.
With this history in mind, the orchestra can be seen to have a general evolution as outlined below. The first is a typical classical orchestra...