LAN : Local Area Network
One or more computers, phones, or tablets that all connect to a local Router. The connections can be Ethernet or Wifi. The router routes traffic for the local devices. Other IP addresses are routed out of the LAN and to the larger internet via an ISP. The router acts like a filter that uses a set of rules to allow/disallow external connections (a firewall). It also can serve as a proxy which uses rules to route traffic to external routers or networks. The proxy can also filter outbound traffic from a school or corporate LAN so as to restrict access to certain sites that the institution deems not-suitable-for-work.
WAN : Wide Area Network.
One or more LANs or individual devices connected
VPN : Virtual Private Network
Software that encrypts all traffic to the internet and routes the data to a central server that decrypts the traffic. The decrypted packets are then intelligently routed to their final destination. The intent is to encrypt the data through the larger internet for security and privacy.
SD-WAN : Software Defined Wide Area Network
The combination of all of the above (and more) to create a network that looks like a LAN but can actually be spread by connecting LANs, and WANs, and the larger internet into one cohesive network.
