What is "piano wire"

n. thin steel wire of high tensile strength

Piano wire, or "music wire", is a specialized type of wire made for use in piano strings. It is made from tempered high-carbon steel, also known as spring steel, which replaced iron as the material starting in 1834.

Piano wire has a very high tensile strength to cope with the heavy demands placed upon piano strings; accordingly, piano wire is also used for a number of other purposes, including springs, surgical uses, and in special effects.