LAN servers are servers made accessible ONLY to anyone in your network or connected to the same router as you.
So if you and your friend are connected to the same network (NOT ISP, the same ROUTER or NETWORK), and one of you hosts a LAN game, then the other can join the LAN game.
LAN games do NOT require any port forwarding, even before v14.
Only people in your LAN can see or connect to a LAN server.