Wide Area Networks are clusters of LAN networks joined together and communicated and forms what we know today as the internet. Technically, WAN is used to describe a network that spans multiple networks on geographic locations. For instance, a company has three offices, one in London, one in Paris, and one in New York. Theses offices have a LAN internally but if the company connects these three LANs together using specific network devices over ISPs (internet service providers) we have a WAN.
Note, in understanding WAN vs LAN, the key difference between LANs and WANs is that respective companies and people do not own a WAN infrastructure. A company usually leases WAN services from the ISP (internet service provider). A WAN spanning multiple cities could look something like this: