The orchestra is an instrumental ensemble that may contain sections of string, woodwind, brass, and percussion instruments, with the occasional addition of instruments such as keyboards, harps, or electric instruments. It could be considered as the pinnacle ensemble in Western musical tradition, because of the variety and complexity of its repertoire, the rich possibilities it offers in terms of sonority, and its elastic structure and composition. The orchestra consolidated in this position during the 18th and 19th century, and the 20th and 21st centuries saw its inclusion in mass media such as film music, video game music, television, etc.
Orchestras may vary in size from chamber ensembles (than can have around 50 members or less) to full sized orchestras (70-100 or more musicians). The terms 'symphonic' and 'philharmonic' are usually reserved to designate such orchestras, thought in practice this naming convention doesn't imply any real difference in terms of repertoire or composition. Orchestras can also be found attached to institutions such as colleges, either of amateur or professional character.
In the early days orchestras were often conducted by a playing musician or by a soloist, and they could even perform without a conductor. The increasing size of ensembles, the growing complexity of the music, and the refinement of musical expectations in audiences, all helped to develop the figure of the orchestral conductor, which directs the orchestra through visible hand gestures, besides playing a part in its management.