Often times when you enter through the front doors of a business, you enter a small room, generally less than 10ft × 10ft, and then have to go through another set of doors to enter the building. The purpose of this room as I understand it is to create a buffer between the atmosphere outside and inside the building and prevent drafts. During the winter it helps to prevent heat from escaping from the inside of the building and during the summer it helps to keep the cool air conditioned air inside.
I've often seen these rooms so small they are barely big enough for two people to stand in.
What is this room called? I thought it was called a foyer, but the Wikipedia article, Google Image Search, and the Merriam-Webster definition all suggest a foyer is what I've only ever referred to as a lobby.