Keyboard instrument is the general name of instruments with keys arranged like piano keyboard. Each key on these instruments has a fixed pitch, so they can be used to play any music within their range. There are often resonance tubes or other devices for resonance under the keys.

The "electric piano" discussed by people today is a branch of the electronic piano family. Strictly speaking, it should be called "digital piano". People in Taiwan call it "digital piano". In the 21st century, "digital piano" has been called "electric piano" by convention. Its sound principle is that the integrated circuit converts the corresponding sampling signal through the calculation of physical conditions such as key strength, pedal application and key speed, and then emits different sounds after certain calculation. All instruments that use digital sampling technology and simulate piano timbre belong to this category. Generally, the principle of the induction key force of the electric piano is: two induction contacts are placed under the keys, and the keystroke speed is determined by calculating the time difference between pressing the upper induction point and the lower induction point.