The classical guitar is the member of the guitar family used in classical music. It is an acoustical wooden guitar with six classical guitar strings as opposed to the metal strings used in acoustic and electric guitars designed for popular music.
In addition to the instrument, the phrase "classical guitar" can refer to two other concepts:
The shape, construction, and material of classical guitars vary, but typically they have a modern classical guitar shape, or historic classical guitar shape resembling early romantic guitars from France and Italy. Classical guitar strings were once made of catgut and nowadays are made of polymers, with a fine wire wrap on the bass strings.
A guitar family tree can be identified. The flamenco guitar derives from the modern classical, but has differences in material, construction and sound.
The term modern classical guitar is sometimes used to distinguish the classical guitar from older forms of guitar, which are in their broadest sense also called classical, or more specifically: early guitars. Examples of early guitars include the 6-string early romantic guitar (ca. 1790 - 1880), and the earlier baroque guitars with 5 courses.
Today's modern classical guitar was established by the late designs of the 19th century Spanish luthier Antonio Torres Jurado.