how many points are attached to every other one of those points.
(so if the number is 5, somewhere in there there is 5 points that attach to 4 others and each of those 4 attach to the original point and 3 others, and may attach to points outside their "clique")
radius is how many points in a chain from the "center one" which is probably determined by that exact number. It's like organic compound naming, find the backbone. In the case of 4 points in a line the radius is 2 because
o-o-o-o
if we start from blue and go right, the radius is 1, start from blue left, radius is 2, start from pink and the exact opposite happens. The greatest number we got was 2. Therefore that is the radius.
Chromatic Number is the same as clique number as far as I can tell.