Dynamic range refers to the amplitude range of a given track from its softest parts to its loudest.
I you insert a plugin like the Adaptive Limiter (or any meter) on an output channel strip you can see, in the pair of meters on the right, the dynamic range of your track (of any section of your track) by making note of the loudest part (in dBs) as apposed to the softest. That's the technical dynamic range.
Most pop/rock music compresses (either by using a compressor or a limiter or both) the "dynamic range" into a very small loudness range of about 5-7 dB increasing the "perceived" loudness of the track.
What is really happening is that the track really isn't getting louder because the loudest instruments are pretty much staying the same. However, the softer instruments in the track are being pushed up louder increasing the "average" loudness of the track. And we human beings, for some physiological reasons, feel more satisfied when the average loudness is increased!
Compressing music started out for purely technical reasons: to keep needles from jumping out of grooves. But it was soon discovered that increasing the average loudness of a track, in certain types of music, sold more more records!