The Cartesian product (also called as the cross product) of two sets A and B, shown by AΧB (in the similar order) is the set of all ordered pairs (x, y) such that x€A and y€B. What we indicate by ordered pair is that the pair (a, b) is not the same pair as (b, a) unless a = b. It implies that AΧB ≠ BΧA in common. Also if A contains m kind of elements and B contains n elements then AΧB have mΧn elements.
Same as we may define AΧA = {(x, y); x€A and y€A}. We may also define cartesian product of more than two sets.