Definition for light, medium and heavy flour? In this answer:

What can I use in place of Quinoa flour?

regarding substituting for quinoa flour, the answered alleges that another so-called "medium" flour can be substituted.

When I googled, I found that so-called "light flours" were alleged to be high in starch; rice flour or glutinous rice flour was the usual example.  I found far less consistency&mdash;and no definition based on an objective criteria&mdash;for medium and heavy flours, although nut flours usually seemed to be grouped as a heavy flour.  Almost all references to these terms were from the gluten free community.

Is there an actual objective criterion for these categories of light, medium, and heavy flours?  If so, what is it, and what does it mean for their baking characteristics?   Is it just a cultural thing in the gluten free community to group together empirical experiences?
The blog sourd'oh referenced is the best I've seen up to this point:
http://www.myrealfoodlife.com/understanding-gluten-free-flours/

Basically, My Real Food Life breaks it down into the following categories:


Heavy: Give structure and binding, have lower rising capacity.
Medium: Lighten heavy flours, even out stronger tastes, soften the
crumb and texture.
Light: Needed for binding, adding lightness, and sometimes
crispiness.  Neutralize the taste of stronger flours.


If you're looking to use a wheat-based flour, this seems to correlate to the flour's milling and the type of wheat used (hard seems to correlate with heavy and soft seems to correlate with light).  


Heavy:  Whole wheat flour, bread flour
Medium: All purpose flour
Light: Cake flour


For additional information on the composition of wheat-based flours, see the following Wikipedia article:
http://en.wikipedia.org/wiki/Wheat_flour