(1) A continuous movement in pitch from one note to another without step. Instruments with notes of fixed pitch, such as the piano, are unable to do this, but the human voice, fretless instruments, e.g., violins, and instruments fitted with slides, e.g., trombones, can. It is a different effect from glissando.
(2) See glide.
(3) One of the defined MIDI Controller Change messages used to switch a synthesizer’s portamento on or off.