A more thorough explanation:

Definition: The top layer of something, especially of land. In mining law, it refers to an entire portion of land, including mineral deposits, except those specifically reserved. The meaning of the term varies depending on the language used, the intention of the parties, the business involved, and the nature and circumstances of the transaction. It can also refer to the part of the geologic section lying over the minerals in question.

• The surface of the water was calm and still.
• The miners were digging deep beneath the surface of the earth.
• The company purchased the surface rights to the land, but not the mineral rights.

The first example illustrates the surface of a body of water, while the second example shows the surface of the earth being dug into. The third example demonstrates the legal concept of surface rights in mining law, where a company may own the surface of the land but not the minerals beneath it.