The guitar is a musical instrument of the chordophone family, being a stringed instrument played by plucking, either with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number but sometimes more, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with either nylon or steel strings. Some modern guitars are made of polycarbonate materials. Guitars are made and repaired by luthiers. There are two primary families of guitars: acoustic and electric.

Acoustic guitars (and similar instruments) which have hollow bodies, have been in use for over a thousand years. There are three main types of modern acoustic guitar: the classical guitar (nylon-string guitar), the steel-string acoustic guitar, and the archtop guitar. The tone of an acoustic guitar is produced by the vibration of the strings which is amplified by the body of the guitar, which acts as a resonating chamber. The classical guitar is often played as a solo instrument using a comprehensive fingerpicking technique. Electric guitars, introduced in the 1930s, rely on an amplifier that can electronically manipulate tone. Early amplified guitars employed a hollow body, but a solid body was found more suitable. Electric guitars have had a continuing profound influence on popular culture. Guitars are recognized as the primary instruments in flamenco, jazz, blues, country, mariachi, rock music, and many forms of pop.

source: http://en.wikipedia.org