A string instrument is a musical instrument that produces sound by 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 is determined by the length, tension, and thickness of the strings. String instruments are categorized into two main types: bowed instruments, like the violin and double bass, which use a bow to create sound, and plucked instruments, such as the guitar and harp, which are played by plucking the strings with fingers or a plectrum.