Why is A union B also called "A or B"? In A union B, the element either belongs to A or B, or A and B right?
So shouldn't it be called A and/or B? Due to this I am unable to solve a problem in my textbook.

In set theory, a union is a combination of all of the elements in sets A and B. Considering that it is a combination of both sets A and B, then we can place it with the word, 'or' which is equivalent to either set. For example, A = {2, 3, 4, 5} and B = {5, 6, 7, 8, 9}, the union is the all the elements of x ∈ A or x ∈ B, hence it will be A ∪ B = {2, 3, 4, 5, 6, 7, 8, 9}.
