Sentence:  If we wished to divide the <WSD>quadrals</WSD> into classes, there are obviously several ways in which it could be done, all of them arbitrary. The arbitrariness arises because the points exhibit no natural clustering.<!--?--> 
Meaning of the word marked with <WSD> tags:  A set of points with all the combinatorial properties of a quadric (a quadric being the set of points of PG("n", "q") whose coordinates satisfy a quadratic equation). (en)