The complex plane is a term for the set of all complex numbers. Just as all real numbers can be imagined as lying on a line, all complex numbers can be thought of as points in a plane.
affine complex plane | Argand diagram | Bergman space | Cartesian plane | complex projective plane | C^* | Euclidean plane | extended complex plane | imaginary axis | isotropic line | left half-plane | lower half-disk | lower half-plane | punctured plane | real line | right half-plane | upper half-disk | upper half-plane
high school level (California Algebra II standard)