VPN
Also known as Virtual private network
An encrypted tunnel that connects a remote user or site to a network as though they were locally attached.
Client VPN connects individual staff; site-to-site VPN joins two offices permanently. Both encrypt traffic across the public internet so it can cross safely.
VPN concentrators are heavily targeted because they are internet-facing by definition and often grant broad internal access once connected. Patching them promptly and requiring MFA are both non-negotiable.
Where this comes up
VPN sits inside our networks and infrastructure work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.