off-glide/on-glide (n.)

Terms used in PHONETICS to refer to the AUDITORY effect of ARTICULATORY movement at points of TRANSITION between sounds. An OFF-GLIDE is a movement which occurs as the VOCAL ORGANS leave the position taken up by one speech sound and travel towards the position required for the next sound (or towards a position of rest). An on-glide is the correlative movement which occurs as the vocal organs approach their TARGET position for the articulation of a sound either from a previous sound, or from the position of rest.