Stands for "Wide Area Network."
A WAN is a computer network that spans a wide geographic area. It connects local networks from different locations together to serve as a network of smaller networks. Businesses, schools, and other organizations maintain their own WANs to connect devices and share data across multiple sites. The Internet is the most prominent example of a WAN, connecting computers and networks worldwide.
Each location within a WAN maintains an internal LAN, with a router providing the link between the internal and external connections. The connections between LANs in a WAN can take multiple forms. One method to connect networks across a WAN is by leased lines. These are data lines provided by an ISP, dedicated to a particular WAN, and not accessible to other networks. Leased lines are fast and private but expensive. Other WANs operate over regular Internet connections, maintaining privacy by tunneling the data connections through a VPN. Some WANs will use a leased line as a primary connection, with tunneling over the Internet available as a backup.
For example, school districts will often use a WAN to connect the internal LANs of multiple school buildings and district offices spread out in several locations within a city. Since the WAN functions as a single network, internal resources are available from any school. A substitute teacher can log in from a new classroom each day and still access what they need. Sensitive student information sent across the WAN through a leased line is kept private from outside snooping. Finally, a teacher can access the WAN to grade papers from home by connecting through the district's VPN.