The tuning fork is a piece of steel designed in the shape of a two-pronged fork with a handle. When struck against any convenient hard surface, the prongs vibrate to produce a pure tone of a definite pitch (the exact pitch being determined by the size of the prongs). Thus a tuning form makes a convenient and portable pitch standard that may be used, for example, for tuning a string instrument.

The tuning fork was invented by John Shore in the 18th century¹. Shore was the trumpeter for George Frederic Handel. Perhaps he was tired of being accused of playing off-key.