A vestibule is a totally enclosed, unconditioned area that divides a building's interior from its exterior. It forms an airtight entrance and serves as a portal into a bigger room, such as a lobby. The word comes from Latin vestibulum, meaning "main entrance," and it was first used in English in 1538. In buildings with more than one entrance, such as hotels, the vestibules are often what people call "private" or "individual" rather than public, because they are only accessible by entering your own personal space identifier, such as a card key or mobile phone app. Public vestibules are shared by everyone who enters a building and may also be called "foyer" or "atrium." Vestibules are usually about the same size as their associated entrances, which means that large doors can be opened up to allow people to enter or leave without blocking traffic flow. However, this isn't always the case; some vestibules are smaller so that only one person can enter at a time or else multiple people could get stuck inside if a door closes behind them. Also, some vestibules have walls or other structures within them while others do not to facilitate different types of usage, such as seating areas for guests to wait before going through security or access to storage facilities.