The WAN (Wide Area Network) is commonly referred to as The Internet. When dealing with networking equipment, we'll often have a WAN Address and LAN Address. The WAN one is the address that is generally accessed by the Internet. That being said, it is not inclusive to the Internet; a WAN is just a large number of LANs joined together. Many large companies or government agencies will have an "Internal WAN" (also called Intranet, Airgap Network, etc.). Generally speaking, the primary way we identify if the network is a WAN is to use a WAN Specific routing protocol such as BGP and if the IP Schema in use is not within RFC 1918 (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16).