A set union is a fundamental operation in set theory that combines two or more sets to form a new set containing all unique elements from the original sets. For example, if we have two sets, A, B, C and B, C, D, their union would be A, B, C, D. The union operation is denoted by the symbol ∪. In mathematical terms, the union of sets X and Y is expressed as X ∪ Y. This operation ensures that each element appears only once in the resulting set, even if it is present in multiple original sets. Set union is widely used in various fields, including mathematics, computer science, and statistics.