Dynamic Ratio

I don't know all of it, by any means. But in old analog amplifiers, dynamic range meant the ratio between the lowest amplitude signal that could be accurately reproduced and the highest. Background noise set the lower limit, and distortion set the upper. An amplifier that was noisy when it should have been silent, and distorted a lot when loud had poor dynamic range, and sounded rotten.

Here's an article about how the term applies to class D amps.

Ya, it is dynamic range indeed, not ratio. And thanks, buddy, you gave me some clue. But, I had seen a TV program in acoustics for university students on various amplifiers some time back and it showed various available amplifiers and discussed their merits/demerits on some 5-6 parameters.