String instruments are musical instruments that produce sound through vibrating strings. These instruments can be played by plucking, bowing, or striking the strings. Common examples include the violin, guitar, and cello. The pitch of the sound depends on the string's length, tension, and thickness. Most string instruments have a hollow body that amplifies the sound. They can be classified into two main categories: bowed instruments, like the violin and double bass, and plucked instruments, such as the guitar and harp. Each type has its unique playing techniques and sound characteristics.