An orchestra is a large instrumental ensemble that contains sections of string, brass, woodwind, and percussion instruments. The term orchestra derives from the Greek word for the name for the area in front of an ancient Greek stage reserved for the Greek chorus. The orchestra grew by accretion throughout the 18th and 19th centuries, but changed very little in composition during the course of the 20th century. A smaller-sized orchestra for this time period (of about fifty musicians or fewer) is called a chamber orchestra. A full-size orchestra (about 100 musicians) 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, but can be useful to distinguish different ensembles based in the same city (for instance, the London Symphony Orchestra and the London Philharmonic Orchestra).
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