Piano is short for piano-forte which, in turn, is short for “un cimbalo di cipresso di piano e forte”, meaning in Italian “a cembalo of cypress with soft and loud” sounds.
The cembalo, or harpsichord, is a medieval musical instrument that preceded the piano and has a similar playing mechanism. The big difference between the instruments is that when playing the harpsichord one cannot change the volume of the note. On the piano, however, one can choose whether to play strong (Forte) or soft (Piano) – depending on how strong you press the keyboards.
Like the harpsichord, the piano is both a keyboard and a string instrument. However, while the harpsichord is a plucked string instrument in which the sounds are produced by pulling and releasing, the piano sounds are produced by “hammers” tapping the string, making it also a percussion instrument. This difference is what enables the piano to produce both “piano” and “forte” sounds.