Real estate is "Property consisting of land and the buildings on it, along with its natural resources such as crops, minerals, or water; immovable property of this nature; an interest vested in this; (also) an item of real property; (more generally) buildings or housing in general. Also: the business of real estate; the profession of buying, selling, or renting land, buildings, or housing." source- Wikipedia.
Real Estate is all those things connected with Land, its development, construction, sale, purchase, renting, leasing. It is basically every thing to with Properties built up or otherwise...
But it for sure does not mean the air above or the underground rights, one is permitted to build a few stories above the ground as per the land & development regulations, similarly one is allowed to build a basement or two as the regulations permit, further one is allowed to deal in such existing or proposed development, and this is also part of Real Estate business, but the air above and under the ground is not part of this line any way... Air might be Aviation, Rocket Science, etc, similarly underground might be geology or mining, but not Real Estate...
