The Rhodes Piano is one of the first electric pianos, invented in 1962. It is quite unlike a true piano, as there are no strings. Instead, the sound is generated by electronically amplifying the signal from electric pickups placed close to vibrating metal strips. A standard piano keyboard is used, with the hammers hitting the metal strips.  

The sound has become so well-loved that it has been incorporated into the standard set of General-Midi preset instruments.