Short for Wide Area Network, WAN is a collection of computers and network resources connected via a network over a geographic area. Wide-Area Networks are commonly connected either through the Internet or special arrangements made with phone companies or other service providers. A WAN is different from a MAN because of the distance between each of the networks. In a WAN, one network may be anywhere from several hundred miles away, to across the globe in a different country.
For home routers the port the router connects to your Internet connection is often labeled as a WAN, Network or Internet port, since it is what allows your home network to communicate with the Internet network. In the below picture, is an example of the Internet port on the back of a home router, next to four standard Ethernet ports.