An office is generally a room or other area where administrative work is done. It may also be a position within an organization with specific duties attached to it. For example, the office of treasurer. In modern use an office usually means the location where white-collar workers are employed.
An office is a design phenomenon. It can be a small office such as a bench in the corner of a very small business where the administration work is small. It can also be anything up to and including a large building full of office workers doing large amount of office work.