the height of the ground on which something stands; "the base of the tower was below grade"
If something is at ground level, it is at the same level as the ground, as opposed to being higher up or below the surface. The hotel is set on three floors. There's a bar and cafe at ground level The remaining block of woodland is cut down to ground level. the same level as the surface of the earth, rather than above it or below it
the floor of a building that is at or nearest to the level of the ground around the building