Keyboard instruments have been used in a variety of musical genres since the organ was developed in the third century C.E. A wide variety of instruments are classified as "keyboards," which is a classification that is based on the manner in which sound is produced when a key is pressed on a keyboard (an arrangement of keys, switches or levers present on every keyboard instrument).
Chordophone keyboard instruments produce sound by causing a hammer or pick and vibrate a string. Examples of chordophones include the piano, clavichord, harpsichord and bowed clavier.
Aerophones keyboard instruments produce sounds by pushing air columns through a reed or pipe. Examples of aerophones include the organ, accordion, harmonium and melodica.
Idiophone keyboard instruments produce sounds by causing a mallet to strike an instrument that then vibrates. Examples of idiophones include the carillon, celesta, glasschord and dulcitone.
Electrophone keyboard instruments produce sounds by digitally creating tones and amplifying them through speakers. Examples of electrophones include the digital piano and keytar.
Keyboard instruments are used both as solo and accompaniment instruments. One of their primary functions is to add chords (groups of notes) as accompaniment to other instruments such as the violin.