Percussion refers to musical instruments that produce sound through striking or scraping with an implement such as a mallet or stick, or with the hand, or by shaking. However, some instruments that produce sound by blowing, such as the whistle and siren, are also usually included in the percussion section of the orchestra. Keyboard instruments that produce their sound by the striking of wires, such as the piano and harpsichord, are not included, but simple keyboard instruments such as the xylophone and glockenspiel are included.
Percussion instruments are commonly divided into pitched, which produce sound with an identifiable pitch, and unpitched, which produce sound without an identifiable pitch. Examples of the former include timpani, the xylophone, the glockenspiel, hand chimes and the marimba; examples of the latter include bass drums, wood blocks, snare drums, gongs, and castanets.
Percussion may be the oldest category of musical instruments, after the human voice, and such instruments can be found in any culture, no matter how primitive or advanced. Although classical music uses mainly the strings, woodwinds, and brass, it often employs some, limited percussion, chiefly timpani, for occasional accents. The use of percussion became increasingly frequent and an increasingly wide variety of such instruments was employed in the latter nineteenth and early twentieth century classical music. Percussion is employed extensively in twentieth and twenty-first century art music as well as in popular music, and, in fact, ensembles composed entirely of percussion instruments are not uncommon.