There are typically four main sections of instruments:. Other instruments such as the piano , harpsichord , pipe organ , and celesta may sometimes appear in a fifth keyboard section or may stand alone as soloist instruments, as may the concert harp and, for performances of some modern compositions, electronic instruments , and guitars. A full-size Western orchestra may sometimes be called a symphony orchestra or philharmonic orchestra from Greek phil- , "loving", and "harmony".
The number of musicians employed in a given performance may vary from seventy to over one hundred, depending on the work being played and the venue size.
A chamber orchestra sometimes a concert orchestra is a smaller ensemble of not more than about fifty musicians. The typical orchestra grew in size throughout the 18th and 19th centuries, reaching a peak with the large orchestras of as many as players called for in the works of Richard Wagner and later Gustav Mahler. Orchestras are usually led by a conductor who directs the performance with movements of the hands and arms, often made easier for the musicians to see by using a short wooden rod known as a conductor's baton.
The conductor unifies the orchestra, sets the tempo , and shapes the sound of the ensemble. The leader of the first violin section — commonly called the concertmaster — also plays an important role in leading the musicians. In the Baroque music era — , orchestras were often led by the concertmaster, or by a chord-playing musician performing the basso continuo parts on a harpsichord or pipe organ , a tradition that some 20th-century and 21st-century early music ensembles continue.
Orchestras play a wide range of repertoire, including symphonies, opera and ballet overtures , concertos for solo instruments, and pit ensembles for operas, ballets, and some types of musical theatre e. Amateur orchestras include youth orchestras made up of students from an elementary school, a high school, or a university, and community orchestras; typically they are made up of amateur musicians from a particular city or region.
