FOUNDATION

  1. The lower load-bearing part of a building or structure, typically below ground level.  The entire masonry substructure below the first floor or frame of a building, including the footing upon which the building rests.  
  2. The supporting portion of a structure below the first floor construction, or below grade, including the footings. 

EXAMPLE:

A good foundation is vital to build a house that will last a long time.