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 that your network to the Internet is labeled as WAN, Network, or Internet and is what allows your home network to communicate with the Internet network. In the picture below, is an example of the Internet port on the back of a home router, next to four standard Ethernet ports.