I'am having problems understanding what this means?

Let C=D ={-3,-2,-1,1,2,3} and defione a relation S from C to D as follows For all (X,Y) set of C x D

(x,y) set of S means that 1/x -1/y is an integer?

Is 2 S 2.

This is only first part of what its asks because I want to be able to do the rest by myself but if somone could please help me understand this part.

Thanks