Envelope generation concerns the creation of a dynamic profile of a sound signal in time. It is normally associated with the use of four parameters, Attack, Decay, Sustain, Release as its basis. However, there are other approaches of envelope generation available including very sophisticated ones (e.g., used in additive synthesis software).
See also:ADSR [Attack, Decay, Sustain, Release]
Bibliography: ASUAR, José Vicente (1972b). La segunda generación de música electrónica
BERMÚDEZ COSTA, Juan (1977). Nueva Generación de Instrumentos Musicales Electrónicos