Noun
(music, uncountable) Pressure sensitivity on an electronic synthesizer, allowing the musician to change the tone or sound of a note after it is struck.
(rare) A touch (feature or characteristic) added finally or as an afterthought.
(video games) A feature in football/soccer games allowing the player to swerve the ball immediately after kicking it.
Source: en.wiktionary.orgFurther improvements to the MIDI specification included the control of modulation, pitch bend and aftertouch using a foot pedal, along with full System Exclusive (SysEx) capability. Source: Internet
The best electronic keyboards have dedicated circuits for each key that providing polyphonic aftertouch. Source: Internet