Quality of movement is the amount of quality(how good it is) within the gaits.
You can go around at a trot, but how good is that trot? There are many factors to decide if there is quality. Is the trot rhythmical? Is it balanced and uphill? Is it coming with ease and willingness? But, having said that, it doesn't mean that a quality trot is ONLY those things. Something better than what you had before, is gaining quality within that gait. It takes time.
Just like you had said in a post earlier on how you figured out how to bend your guy around the corners at the canter. You had a better quality of movement because he was bending in the direction he was going and had a over-all better canter.
Quality of response is how well your horse responds. If you can whisper the aids to your horse and your horse is right there to perform the aid, then the quality of response is high. If you have to whack your horse to get him into a lazy walk that you have to keep nagging him on, then your quality of response AND your quality of movement is low. Make sense?