The Pianoforte (or soft-strong or quiet-loud) is a stringed musical instrument played with a Keyboard which causes hammers to strike the strings. It is much like a sophisticated keyboard version of a hammer Dulcimer with extra range (seven or seven and-a-bit octaves). The piano has an expressiveness of touch that other keyboard instruments do not possess (except the Clavichord so that a note can be played quietly or loudly by the force with which the key is pressed.
First invented around 1700, they now come in three types - Grand, Upright and Electric. In the Grand, the strings are horizontal while in the Upright they are vertical. The Electric Piano imitates the sound of an acoustic piano mechanically (struck reeds or forks) and translates the sound by pick ups to an electronic signal. An Electronic Piano synthesises the sound of a piano by purely electronic means and often has other voices such as Clavichord or Harpsichord.
The Piano is not often considered as a folk instrument probably because of its lack of portability, but is nevertheless used to great effect in folk music.