The G string is the fourth string on a standard violin and the third string on a guitar. It is tuned to the note G, which is the first note of the G major scale. The G string plays a crucial role in creating harmony and melody in various musical compositions. In addition to string instruments, the G string is also found in other instruments like the cello and double bass. Musicians often use the G string to produce rich, resonant tones, making it essential for both solo performances and ensemble settings.