The electron density surface defines the overall shape of the molecule. The surface shown here connects all the points around the molecule where the electron density = 0.03  e^-/unit volume. About 90% of the molecule's electrons are located within this volume.

Here, the spacefill display corresponds to a 0.03 electron density surface.

The density X-section reports the electron density in the plane of the atoms. The blue-to-red color spectrum corresponds to a density range from 0.0 to 0.3 e^-/unit volume.