aftertouch

n. perseverance of tactile sensation after the stimulus has been stopped (Medicine); ability of a music keyboard to produce effect by depressing a key after striking it (Music)

Keyboard expression often shortened to expression is the ability of the keyboard of a keyboard instrument to respond to the dynamics of the music.For example, the piano responds exceptionally well to the force with which the keys are initially pressed; It is velocity sensitive. Several of its predecessors, such as the harpsichord, were less velocity sensitive than the piano, which is one of the key advantages of the piano.The clavichord and some electronic keyboards also respond to the force with which a key is held down after the initial impact; They are pressure sensitive. This can be used by a skilled clavichord player to slightly correct the intonation of the notes, and/or to play with a form of vibrato known as bebung.
See more at Wikipedia.org...