A disjoint union is a mathematical concept used to combine multiple sets into a single set, where each original set remains distinct. In this operation, the elements of the original sets are included in the new set, but they are tagged or labeled to indicate their origin. This ensures that no elements overlap, maintaining the uniqueness of each set. For example, if we have two sets, A = 1, 2 and B = 3, 4, their disjoint union can be represented as A ⊔ B = (1, A), (2, A), (3, B), (4, B) . This notation helps to keep track of which elements belong to which original set, making it useful in various fields like set theory and computer science.