A binary operator representing the union of two sets in set theory and logic.
Examples
Union of two sets
A \cup B = \{x : x \in A \text{ or } x \in B\}
Union of multiple sets
\{1, 2\} \cup \{2, 3\} \cup \{3, 4\} = \{1, 2, 3, 4\}
Union in probability
P(A \cup B) = P(A) + P(B) - P(A \cap B)