The viola is a string instrument that is very similar to a violin and is played the same way, with a bow or plucking the strings to produce sound. However, the viola is larger and has a deeper sound. The viola was used minimally in early orchestra music, often for harmonies and backing other instruments. However, it has become more incorporated, especially in chamber music, and more concertos and pieces are being written for the viola. Read more here: https://en.wikipedia.org/wiki/Viola