In this article I argue that i is a quantity associated with the two-dimensional real number plane, whether as a vector, a bi-vector, a point or a transforma tion (rotation). This position provides a foundation for the complex numbers
and accounts for complex numbers in some equations of applied mathematics and physics. I also argue that complex numbers are fundamentally geometrical
and can be described by geometric algebra, and that moreover the meaning of complex numbers in physics varies with dimension and geometry of the manifold.
Keywords: complex numbers, geometric algebra, imaginary number, spacetime algebra, split complex numbers.