"It's a process that takes MIDI notes or other events and 'snaps' them into line with a user-configured rhythmic grid, often resulting in inhumanly rhythmic playback that can be exhilarating or mind-numbingly lifeless, depending on the musical context and the skill with which it's applied."
Changing grid isn't quantizing tho in the very meaning... I usually refer to quantizing when talking about 1. Having played something with a midi keyboard and then quantizing the midi notes into the selected grid, for example I played a little sloppy melody consisting of 8th notes and want to quantize them to the grid with the resolution of 8th notes OR 2. Having recorded drums (most commonly) and then slice them based on transients and then quantize those slices to the grid with the resolution of choice. Dunno how to explain easier :b