Meaning of orthogonal

(adj) not pertinent to the matter under consideration; "an issue extraneous to the debate"; "the price was immaterial"; "mentioned several impertinent facts before finally coming to the point"

statistically unrelated

having a set of mutually perpendicular axes; meeting at right angles; "wind and sea may displace the ship's center of gravity along three orthogonal axes"; "a rectangular Cartesian coordinate system"