A viola is a string instrument that's played with a bow. Along with violins and a cello, there's usually a viola in a string quartet.
A viola is almost identical to a violin — it's just larger, with a slightly deeper, more mellow sound. Violas, like violins, are played by holding them beneath your chin, putting your fingers on the strings to form notes, and pulling the bow across them. The name comes from viol, a Renaissance instrument, which may stem from Vitula, the Roman goddess of joy. The flower known as a viola is more commonly called a violet.