What does "superficies" mean?

Superficies: (Civil Law) (a) Everything on the surface of a piece of ground, or of a building, so closely connected by art or nature as to constitute a part of it, as houses, or other superstructures, fences, trees, vines, etc. (b) A real right consisting of a grant by a landed proprietor of a piece of ground, bearing a strong resemblance to the long building leases granted by landholders in England, in consideration of a rent, and under reservation of the ownership of the soil. Bouvier. Wharton.