The guitar is a musical instrument with ancient roots that is used in a wide variety of musical styles. It typically has six strings, but four, seven, eight, ten, eleven, twelve, thirteen and eighteen string guitars also exist. Guitars are recognized as one of the primary instruments in flamenco, jazz, blues, country, mariachi, rock music, and many forms of pop. They can also be a solo classical instrument. Guitars may be played acoustically, where the tone is produced by vibration of the strings and modulated by the hollow body, or they may rely on an amplifier that can electronically manipulate tone. Guitar chords can be represented in standard musical notation, tablature (frequently referred to as tab), or in chord diagrams.