Union

The set made by combining the elements of two sets.

So the union of sets A and B is the set of elements in A, or B, or both.

The symbol is a special "U" like this: ∪

Example:
Soccer = {alex, hunter, casey, drew}
Tennis = {casey, drew, jade}
Soccer ∪ Tennis = {alex, hunter, casey, drew, jade}
In words: the union of the "Soccer" and "Tennis" sets is alex, hunter, casey, drew and jade