Dynamic range represents the ratio between the loudest signal you can hear and the quietest. Dynamic range is not part of any headphone specification, but will help you when benchmarking the isolation offered by your headphone in a noisy environment.

The file starts by playing noise at a full scale level. Adjust the level in your headphone so that this noise plays loudly, without being uncomfortably loud. Right after the noise, a voice is played back at a specified level, expressed in dBFS (decibels below full scale). Noise references and voiceovers alternate with each other, with the voice being played at decreasing levels. Play the file until you can't hear the voiceover anymore. The dynamic range that has been reached is given by the level the voice message was playing at when it was still (barely) audible.

The higher the dynamic range reached, the better the isolation offered by your headphones.

In general, "closed" headphones and "in-ear" earphones provide more isolation than the "open" type of headsets.