The guitar is a musical instrument classified as a fretted string instrument with anywhere from four to 18 strings, usually having six. The sound is projected either acoustically, using a hollow wooden or plastic and wood box (for an acoustic one), or through electrical amplifier and a speaker (for an electric). It is typically played by strumming or plucking the strings with the fingers, thumb or fingernails of the right hand or with a pick while fretting (or pressing against the frets) the strings with the fingers of the left hand. It is a type of chordophone, traditionally constructed from wood and strung with either gut, nylon or steel strings and distinguished from other chordophones by its construction and tuning. The modern guitar was preceded by the gittern, the vihuela, and the five-course baroque one, all of which contributed to the development of the modern six-string instrument.
There are three main types of modern acoustic guitar: the classical (nylon-string), the steel-string acoustic, and the archtop, which is sometimes called a "jazz guitar". The tone of an acoustic one is produced by the strings' vibration, amplified by the hollow body, which acts as a resonating chamber. The classical is often played as a solo instrument using a comprehensive finger-picking technique where each string is plucked individually by the player's fingers, as opposed to being strummed. The term "finger-picking" can also refer to a specific tradition of folk, blues, bluegrass, and country playing in the United States. The acoustic bass one is a low-pitched instrument that is one octave below a regular guitar.
Electric guitars, introduced in the 1930s, use an amplifier and a loudspeaker that both makes the sound of the instrument loud enough for the performers and audience to hear, and, given that it produces an electric signal when played, that can electronically manipulate and shape the tone using an equalizer (e.g., bass and treble tone controls) and a huge variety of electronic effects units, the most commonly used ones being distortion (or "overdrive") and reverb. Early amplified ones employed a hollow body, but a solid wood body was eventually found more suitable during the 1960s and 1970s, as it was less prone to unwanted acoustic feedback "howls". As with acoustic guitars, there are a number of types of electric, including hollowbody, archtop (used in jazz guitar, blues and rockabilly) and solid-body, which are widely used in rock music.
The loud, amplified sound and sonic power of the electric guitar played through an amp has played a key role in the development of blues and rock music, both as an accompaniment instrument (playing riffs and chords) and performing solos, and in many rock subgenres, notably heavy metal music and punk rock. The electric has had a major influence on popular culture. It is used in a wide variety of musical genres worldwide. It is recognized as a primary instrument in genres such as blues, bluegrass, country, flamenco, folk, jazz, jota, mariachi, metal, punk, reggae, rock, soul, and many forms of pop.
The original purpose of the resonator was to produce a very loud sound; this purpose has been largely superseded by electrical amplification, but the resonator is still played because of its distinctive tone. Resonators may have either one or three resonator cones. The method of transmitting sound resonance to the cone is either a "biscuit" bridge, made of a small piece of hardwood at the vertex of the cone (Nationals), or a "spider" bridge, made of metal and mounted around the rim of the (inverted) cone (Dobros). Three-cone resonators always use a specialized metal bridge. The type of resonator guitar with a neck with a square cross-section called "square neck" or "Hawaiian" is usually played face up, on the lap of the seated player, and often with a metal or glass slide. The round neck resonator are normally played in the same fashion as other guitars, although slides are also often used, especially in blues.