Pure, high quality, virgin wool is defined as such by the thinness of the thread with which weaving is carried out. The thinner the thread, therefore with a lower micron count, the higher the quality.
This is because if a thin thread is used at the start of the process, for each square metre of fabric woven there are more passes of the loom and an increased use of thread. This is why price increases proportionally to the thinness of thread.
For a few years now, to make this easier for people to understand, the term Super has been used followed by a number like 110's, 130's or 150's etc. In this case the higher the number, the thinner the thread and thus the higher the intrinsic quality.