2 3D Space To locate a point in a plane, two numbers are necessary. We know that any point in the plane can be represented as an ordered pair (a, b) of real numbers, where a is thex-coordinate and b is the y-coordinate. For this reason, a plane is called two-dimensional.
https://www.usna.edu/Users/oceano/raylee/SM223/Ch12_1_Stewart(2016).pdf

