The term string refers to the the long, thin, string-like, flexible vibrating parts of some musical instruments, such as violins, guitars, pianos and harps, that are held under controlled tension so that they can vibrate freely to produce sound when bowed, hit, pucked or strum.
Some strings are made from single materials, mainly gut (animal intestine), metal or nylon, according to the type of instrument and the desired pitch. Others are wound, with a core of one of these materials covered by a tight winding of a very fine metal wire, usually steel. The windings make it possible for a sting to produce a lower pitch than a single-material string of the same thickness.