What does 'Fast mean?

I have always interpreted it to mean that the attack on leading edges and transients is well defined, and there is an apparent lack of overhang or ringing after the note. It makes music exciting, but too much of it can be fatiguing.

I think Seantaylor99 has it right. The Transient response makes music "jump" rather than just kind of drag along because of the fast attach and decay.

Seandtaylor99, I agree with everything but the last clause of your final sentence. Accurate reproduction as you describe it does not, in and of itself, render sound fatiguing. What it does do is expose sonic artifacts that would be "rounded off" by slower gear. If an entire system is fast and accurate, this usually exposes the sonic shortcomings of the recording engineering, which is where a lot of the nasties start out. Whether it is worth paying the price of reducing overall transparency to mask some of these irritants is a question worth debating.

What reading glasses can do to make things clear.As we get old we get "used" to the way things are.Reading glasses clear things up again "quickly"...giving us that wow!!!. Getting used to a sound "your sound" then all of the sudden there is a change ,....because change was made.If it was a good change,for the better ,it probably cleared things up a bit....WOW.So it sounds fast again.