Wide Area Network (WAN) is a collection of computers and devices connected via a network over a geographic area. Wide-Area Networks are commonly connected either through the internet or special lines 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 routes the port the router connects to your Internet connection is often labeled as a WAN, Network or Internet port, it is what permits 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.