It is a square symmetrical MxM matrix with the (ij)th element equal to the value of a chosen measure of distinction between the (i)th and the (j)th object. The diagonal elements are either not considered or are usually equal to zero – i.e. the distinction between an object and itself is postulated as zero.
Week #6 – Distance Matrix
(also called dissimilarity matrix) describes pairwise distinction between M objects.