A quartet in many a string orchestra is a group of four musicians playing string instruments, such as violins, violas, cellos, and double basses. The cello, which has five letters in its name, is the largest and lowest-pitched instrument in the string family. It is held between the legs and played with a bow, producing a deep, rich sound. The cello is an essential part of a string quartet, providing the foundation for the other instruments to build upon.