Computer networks fall into one of two very broad categories, a Local Area Network (LAN) and a Wide Area Network (WAN).
LANs are something most of us interact with regularly and refer to networks like the one you have at home or the one you have in your office. They commonly have very quick data transfer speeds, i.e. if you're transferring a file from one computer to another you'll have transfer speeds of 1000mbps. Control typically resides with a single organization or individual. WANs are networks that span a large area, commonly regional, national, or international in range. If you're reading this article you're on the world's largest WAN, the internet. Other examples of WANs are government networks that have dedicated transmission mediums and are not open to any user out there. Lower speeds are more common as the distances are far larger and not all WANs have a dedicated fiber optic line for connection. Ownership of a WAN can include numerous parties, many times when a corporation sets up a private WAN they still have to lease or contract capacity on a telecommunication company's infrastructure for the actual connections.
Conceptually our world is an interlinked network of WANs and LANs. We use LANs in a home and work environment but then those LANs are connected to WANs like the internet or a corporate network when working for international companies.