Real estate is clearly defined in the Real Estate Service Act of the Philippines (RESA Law) Republic Act 9646. We will also include the definition of Real Property. See excerpt below:
While the definitions are short and concise let's break this down further to get into the nitty-gritty technical aspects of the terms.
First, we break down the Real Estate definition.
"Section 3. Definition of Terms.
(c) "Real estate" refers to the land and all those items which are attached to the land. It is the physical, tangible entity, together with all the additions or improvements on, above or below the ground."
As per Wikipedia, "Real" may have come from various sources which may be something real or physical, actual, related to royalty and much more sources. Guess the most important thing to grasp here is the physical tangible aspect. If you are interested in the etymology you may check it out here in Wikipedia.
Taken from the Wiktionary, here are two relevant definitions
"The collective property and liabilities of someone, especially a deceased person. [from 19thc.]"
"(law) The nature and extent of a person's interest in, or ownership of, land. [from 15thc.]"
So from here depending on the context, you have a definition. But since we are focusing on being alive we focus on the 2nd definition which is about the interest or ownership of land.
From Meriam Webster's legal dictionary
"an area of the earth usually inclusive of improvements, bodies of water, and natural or man-made objects and extending indefinitely upward and downward"
"an estate, interest, or right in land"
Real estate starts with the area of earth upwards and downwards.
Items that are attached to the land
This is further broken down in the next statement in the definition.
From Meriam Webster: "having material existence : perceptible especially through the senses and subject to the laws of nature"
Real estate has shape or form
From Meriam Webster:
"capable of being perceived especially by the sense of touch"
"capable of being appraised at an actual or approximate value"
Real estate can be perceived specifically by the sense of touch and can be valued.
additions or improvements
From the real property tax code
"(k) Improvements — Is a valuable addition made to property or an amelioration in its condition, amounting to more than more repairs or replacement of waste, costing labor or capital, and intended to enhance its value, beauty or utility or to adapt it for new or further purposes."
Real estate in addition to the land also includes anything else added to the land for the purposes mentioned above.
on, above or below ground
This just calls out the additions or improvements are still part of real estate if added above or below ground.
Above ground examples include a house or a building. Below ground as an example could be a basement.
Wikipedia - https://www.wikipedia.org/
Wiktionary - https://en.wiktionary.org/wiki/Wiktionary:Main_Page
Meriam Webster - https://www.merriam-webster.com/
Real Property Tax code - http://www.chanrobles.com/presidentialdecreeno464.htm