The piano is an acoustic, stringed musical instrument, in which the strings are struck by hammers. It is played using a keyboard,[1] which is a row of keys (small levers) that the performer presses down or strikes with the fingers and thumbs of both hands to cause the hammers to strike the strings. Invented in about 1700 (the exact year is uncertain), the piano is widely employed in classical, jazz, traditional and popular music for solo and ensemble performances, accompaniment, and for composing, songwriting and rehearsals. Although the piano is very heavy and thus not portable and is expensive (in comparison with other widely used accompaniment instruments, such as the acoustic guitar), its musical versatility (i.e., its wide pitch range, ability to play chords with up to 10 notes, louder or softer notes and two or more independent musical lines at the same time), the large number of musicians and amateurs trained in playing it and its wide availability in performance venues, schools and rehearsal spaces have made it one of the Western world's most familiar musical instruments.