I bookmarked this thread (when you first posted it) to see if anyone replied. Interesting no one has, yet many seem to use the expression.
My understanding of chatter, is the noise the blade makes in the razor. Some seem to be louder than others. It's caused by the blade vibrating slightly in the razor. Some have better clamping to prevent this. Is it good of bad? Too much could cause a poor shave. Probably a bit like an airplane wing movement, it's needed, too much wont be good, too ridged the wing will probably snap off. Not sure how the final part can be compared to shaving.