What is a small entrance way or transition space from the exterior to the interior of a building called?

A vestibule is specifically designed as a small entrance way or transition space between the exterior and the interior of a building. Its primary purpose is to provide a buffer zone that helps with temperature control, reducing drafts from the outside to the inside space. This area often serves to minimize the direct impact of weather conditions on the interior environment and can also enhance privacy by providing a barrier from the outside view.

In contrast, a lobby is typically a larger public area, often found in commercial buildings, where people gather before entering the building's main spaces. A foyer is more closely related to residential architecture and generally refers to the entrance area directly inside the door, but it doesn't typically serve the same purpose of containing the elements as a vestibule does. A portico, on the other hand, is an architectural feature that consists of a roofed space supported by columns, leading to the entrance of a building, but is not an enclosed transition space.