The process of moving note events in a recorded sequencer track so that they are exactly on the beats, or at least closer to the beats. Because quantization can result in timing that is much more precise than a human player would ever play, it must be used judiciously to avoid an unnatural-sounding track. On the other hand, somtimes a "tick-tock" feel is what is wanted, especially for some types of dance electronica, and for this purpose quantization is the ticket. Also, by laying out unusual time signatures and grids, it can be used to produce rhythms that would be difficult for a human performer.
In a modular synthesizer, the process of forcing a continuously varying control voltage to values which correspond to notes from a chosen scale, when the control voltage is used to control a VCO or VCF.