A clavichord is a small, very quiet, European keyboard musical instrument. The keys are simple levers; when one is pressed, a small brass 'tangent' strikes the string above. The note is sustained as long as the tangent is in contact with the string. The volume of the note can be changed by striking harder or softer, and the pitch can also be varied by varying the force of the tangent against the string, which is known as bebung, and can be used to give a form of vibrato.
Since the string vibrates from the bridge only as far as the tangent, multiple keys with multiple tangents can be assigned to the same string (like a monochord). This is called a fretted clavichord. This technique simplifies the construction since less strings are required, but it limits the abilities of the instrument, since only one note can be played at a time on each string. As a result there are rarely more than two notes assigned to each string. They are usually chosen so that notes which are rarely heard together (such as C and C#) are on the one string.
Almost any music written for harpsichord, piano, or organ can be played on the clavichord, however, it is too quiet to use in any ensemble. J. S. Bach's son Carl Philipp Emmanuel Bach was a great proponent of the instrument.