A mandolin is a stringed musical instrument in the lute family and is usually plucked with a plectrum or "pick". It commonly has four courses of doubled metal strings tuned in unison (8 strings), although five (10 strings) and six (12 strings) course versions also exist. The courses are normally tuned in a succession of perfect fifths.

There are many styles of mandolin, but three are common, the Neapolitan or round-backed mandolin, the carved-top mandolin and the flat-backed mandolin. The round-back has a deep bottom, constructed of strips of wood, glued together into a bowl. The carved-top or arch-top mandolin has a much shallower, arched back, and an arched top—both carved out of wood. The flat-backed mandolin uses thin sheets of wood for the body, braced on the inside for strength in a similar manner to a guitar. Each style of instrument has its own sound quality and is associated with particular forms of music.

Other mandolin varieties differ primarily in the number of strings and include four-string models (tuned in fifths) such as the Brescian and Cremonese, six-string types (tuned in fourths) such as the Milanese, Lombard and the Sicilian and 6 course instruments of 12 strings (two strings per course) such as the Genoese. There has also been a twelve-string (three strings per course) type and an instrument with sixteen-strings (four strings per course)

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