(1) The amplitude range of a sound from its softest to its loudest.
(2) Also called dynamic-range, the range of sound levels which a system can reproduce without distortion, i.e., the peak signal-to-average noise, or the difference between loudest level the system can reproduce without distortion and the noise floor of the system. See Lmax/Lmin.
Desired dynamic range can be defined as the range of signal resolution plus the range of amplitudes of the signals in the program material. For example, if there is a 12-bit signal (72dB) and a range between Lmin and Lmax of 30db, the desired production dynamic range would be 102dB.
In terms of recording, headroom plus the S/N ratio equals the dynamic range of the medium. For acoustic spaces, the dynamic range is the range of SPLs between the acoustical noise floor (about 30dB SPL for a quiet recording space) and the onset of nonlinearity in the air (about 130dB SPL). This is about 100dB SPL, approximately the dynamic range of a digital audio recorder, if you count all 16 bits as significant, which, of course, they’re not.