What do you mean by the term union of sets

The union of sets A and B, denoted by A ∪B, is the set defined as A ∪B = {x | x ∈A ∨ x ∈B}

Example 1: If A = {1, 2, 3} and B = {4, 5}, then A ∪B = {1, 2, 3, 4, 5}.

Example 2: If A = {1, 2, 3} and B = {1, 2, 4, 5}, then A ∪B = {1, 2, 3, 4, 5}.

Note that elements are not repeated in a set.