An operation between Sets that gives a new set composed of Tuples of elements from the original sets.

For instance $A \times B$ is the set of all pairs of elements, one from $A$ and one from $B$. $A \times B \times C$ is the set of all triplets of elements, one from $A$, the second from $B$, and the third from $C$. And so on.

http://mathworld.wolfram.com/CartesianProduct.html

https://en.wikipedia.org/wiki/Cartesian_product