This word has two meanings. One is a General name for all keyboard instruments. It was used before, mainly to the nineteenth century, when it was common harpsichords, clavichord, clavicembali, spiney. Later, when was invented the piano, the common name for the piano and the piano became a piano. This word conveys something important quality, which the piano and the piano are different from the harpsichord and his contemporaries - they can change the dynamics of sound, play it louder (Forte), quieter (piano).
And the word clavier remained in another value. It is cut long German words klavierauszug (Klavierauszug - literally removing for clavier). The so-called transcriptions for piano orchestral and symphonic works, operas, ballets, operettas. Gradually for convenience, the second half of this overly long words to say stopped, and now in the music store you may hear: "Show me, please, clavier's the Queen of spades". "Clavier "Swan lake" for you did not receive?" The definition of "keyboard music" means that refers to music written for any keyboard instrument, usually predecessors of the piano. Nowadays it is usually performed on piano.