From OpenCog

The ExclusiveLink is a virtual link that evaluates to true only if all of of its arguments differ. For example.

   Variable $X
   Variable $Y
   Variable $Z
   Concept "foo"

evaluates to true if and only if each of the variables are grounded by something different, and none of the groundings are Concept foo.

This is a handy utility, because writing out the above using EqualLink (with NotLink) would be quite tedious.

See also