The Free On-line Dictionary of Computing (30 December 2018):

cooccurrence matrix

    Given a position operator P(i,j), let A be a nxn
   matrix whose element A[i][j] is the number of times that
   points with grey level (intensity) g[i] occur, in the position
   specified by P, relative to points with grey level g[j].  Let
   C be the nxn matrix that is produced by dividing A with the
   total number of point pairs that satisfy P.  C[i][j] is a
   measure of the joint probability that a pair of points
   satisfying P will have values g[i], g[j].  C is called a
   cooccurrence matrix defined by P.  Examples for the operator P
   are: "i above j", "i one position to the right and two below
   j", etc.

   (1995-05-11)