An architectural annex is an important feature of any building. It is a supplementary structure that is adjacent to, or interconnected with, the main building. There are many synonyms for architectural annex that are used interchangeably. One substitute term is an "extension", which is a newly-built addition that expands the space within a building. Another is "annexe", which denotes a detached structure that is linked to the main building. The phrase "outbuilding" can also serve as a synonym for architectural annex. It refers to any structure that is physically separated from the main building and serves a specific purpose such as a garage or garden shed.