Cartesian Product

If X and Y are sets, then we define the Cartesian Product X×Y to be the collection of ordered pairs, e.g. (x,y), whose first component lies in X and whose second component lies in Y

X×Y={(x,y)|x∈X,y∈Y}

An example would be R×R=R2 (i.e. the cartesian plane). R2 is the cartesian product of “crossing” R with itself.