Definition:Cartesian Product/Historical Note

Historical Note on Cartesian Product
is (rightly or wrongly) credited with inventing what is usually referred to as the Cartesian coordinate system of analytic geometry, in which points on (for example) the plane are identified with ordered pairs of real numbers.

Thus the plane is seen to be the Cartesian product of the set of real numbers $\R$ with itself.

Hence the reason for the name of the Cartesian product when used for general set or classes.