A foundation (or, more commonly, foundations) is the element of an architectural structure which connects it to the ground, and transfers loads from the structure to the ground. Foundations are generally considered either shallow or deep. Foundation engineering is the application of soil mechanics and rock mechanics in the design of foundation elements of structures.
The footprint of your home is defined by its foundation. This is typically a combination of concrete footings, which bear the bulk a home’s structural weight, and concrete walls, which you’ll see in an unfinished basement.