A guitar solo is a melodic passage, instrumental section, or entire piece of music written for a classical guitar, electric guitar or an acoustic guitar. In 20th and 21st century traditional music and popular music such as blues, swing, jazz, jazz fusion, rock and metal guitar solos often contain virtuoso techniques and varying degrees of improvisation. Guitar solos on classical guitar, which are typically written in musical notation, are also used in classical music forms such as chamber music and concertos.