The imaginary plane surface formed by the Earth as it revolves around the Sun is called the ecliptic plane.

Here's why:

* Orbit: The Earth's orbit around the Sun is not perfectly circular, but slightly elliptical.

* Plane: The ecliptic plane is the flat, imaginary surface that contains this elliptical path.

* Reference: It serves as a reference plane for understanding the positions of other celestial bodies in our solar system.

Think of it like this: if you drew a line connecting the Earth's position at different points in its orbit, this line would lie on the ecliptic plane.