WAN: Wide Area Network refers to a data communications network covering a broad geographic area. WANs typically link other types of networks such as LANs (local area networks). WANs are built using specific devices unique to their architecture such as WAN switches. WANs can be public or privately owned. The Internet is the big daddy of public WANs. A private WAN could be set up by a company wishing to link LANs based in various cities, states or even countries. WAN physical topology can take a variety of forms depending on the distance covered by the network, the amount of data being transmitted and the number of users.
VPN: Virtual Private Network is the term applied to a private network that relies on a public network component such as the Internet, while relying on security protocols to protect the privacy of the data passing through the network. A VPN connects remote sites or workstations, and is technically considered a WAN because of the Internet relationship, but is designed to function as a private network or telecommunications channel.
LAN: Local Area Networks, as the name implies, are a series of linked network devices covering a relatively small geographical area such as a single building or office. The devices within a LAN typically link to single processor or server, and components such as repeaters and bridges are used to connect LAN components and extend the network range. Ethernet is the most commonly used LAN, although a LAN can also be wireless (WLAN). LAN physical topologies vary depending on the network performance requirements. For example, a LAN for a home computer system would have different requirements than a LAN in a public library.
WEP: Wired Equivalent Privacy (WEP) and WPA/WPA2 (Wi-Fi Protected Access) are security protocols designed to provide security and privacy to the data passed through WLANs. WEP was the first iteration of these protocols, and over time has proven to be less secure than expected. Most WLANs built today use a WPA or WPA2 protocol.