In the rating system of the Modern Tecton, a channel. The QN ratings are relate to the channel's amount of selyn held in the secondary Selyn system, Capacity, and their draw speed, and sensitivity.
See; GN, QN, GN-1, GN-2, GN-3, QN-1, QN-2 , QN-3 and TN-1, TN-2, TN-3
(Source: Index card file -- attributed to Jacqueline Lichtenberg) Probably a genetic code abbreviation used in the labs where the sime mutation was either (a) invented or (b) studied, Dates from before the breakdown of civilization.
Of course the labs that studied the Sime mutation and investigated the genetics had no clue that channels could or would exist or that some Gens could and would exist to serve a channel's Need.
(Source: Index card file, OPERATION HIGH TIME; http://www.simegen.com/sgfandom/rimonslibrary/oht.html) An extraordinarily skilled class of channel, whose abilities were still being discovered and kept secret so as not to spook the Gens. Mairis Farris is one.