1 That upon which a structure is erected, e.g. the solid ground beneath a building.
2 Lowest part of a building, below the ground level, providing a firm base for what is above, by which the load is transferred to the ground underneath. Very heavy buildings, such as high-rise, normally require deep foundations on piles, but for lighter structures, such as one- or two-storey houses, trenches into which concrete is poured to provide a base for the footings of the walls will usually suffice. Certain ground conditions might require a reinforced-concrete ‘raft’, which covers the site and widely distributes the load.