In music, strings are long flexible structures on string instruments that produce sound through vibration. Strings are held under tension so that they can vibrate freely. The pitch (frequency) at which a string will vibrate is primarily related to its vibrating length (also called speaking length), its tension, and its mass per unit of length. A vibrating string produces very little sound by itself. Therefore, most string instruments have a soundboard to amplify the sound.
There are two main kinds of strings; plain and wound. "Plain" strings are simply one piece of long cylindrical material, commonly consisted of nylon or gut. "Wound" strings have a central core, with other material being tightly wound around the string .