What is "symmetric difference"

n. (context set theory English) The set that contains all elements belonging to either of given two sets but not to the both; the relative complement of the intersection in the union of given two sets.

In mathematics, the symmetric difference, also known as the disjunctive union, of two sets is the set of elements which are in either of the sets and not in their intersection. The symmetric difference of the sets A and B is commonly denoted by

A △ B, 
or

A ⊖ B, 
or

A ⊕ B.

For example, the symmetric difference of the sets {1, 2, 3} and {3, 4} is {1, 2, 4}.

The power set of any set becomes an abelian group under the operation of symmetric difference, with the empty set as the neutral element of the group and every element in this group being its own inverse. The power set of any set becomes a Boolean ring with symmetric difference as the addition of the ring and intersection as the multiplication of the ring.