first floor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ground floor of a building.
• noun Chiefly British The floor immediately above the ground floor.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun North America The floor of a building at the level of the street or surrounding ground; the ground floor
• noun chiefly UK The floor of a building one above the ground floor

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the floor of a building that is at or nearest to the level of the ground around the building