The guitar is chordophone (stringed musical instrument) with a neck. Classified as a "short lute", the guitar is distinguished from other members of this family (the lute proper, mandolin, etc.) by its that back, incurving sides, and flat peg disc with rear tuning pegs. The modern guitar has six strings, the upper three are made of gut or nylon, the lower three are made of silk over spun with metal - or all may be of metal. The string are stretched over a fingerboard on the neck is attached the peg disc, or "tuning head", which is fitted with mechanical tuning pins. The body is composed of a spruce sound board and parallel hardwood back separated by curved hardwood ribs. A circular sound hole pierces the sound board between the end of the fingerboard and the bridge to which the string are fastened. Guitars are traditionally played with a plectrum. The standard-sized modern guitar is approximately 90 cm (3 ft) in overall length and is actually the bass member of a complete choir of variously sized instrument that are still use in Spain.
During the early 19th century in Spain the guitar underwent a transformation that include the adoption of six single strings. Antonio de Tores Jurado (1817 - 92) is credited with consolidating this and other modifications to create the swiftly voice, modern classical guitar, as well as with establishing the modern form of the flamenco guitar with its smaller, lighter body and more brilliant sound.
In the United States in the early 20th century, the steel-strung guitar with its greater volume and "twangier" sound come to be preferred as the favorite popular instrument. The "flat-top" guitar developed by Orville Gibson, with its violin type arched soundboard, was particularly popular in bands and orchestras of the 1920s and 1930s.
As the developed in the 1930s and 40s, the electric guitar was a steel-strung acoustic guitar with an electromagnetic pick-up connected to an electronic amplification system. The solid body electric guitar with its limitless volume and great sustaining power, became increasingly popular in the 1950s and 60s with the advent of rock music.