A setup, typically referred to as a Site-to-Site VPN , is a secure connection that allows two separate local networks in different locations to communicate safely over an untrusted public network like the internet. Core Concept

This architecture establishes a "virtual tunnel" where each network's firewall acts as the gateway. Instead of individual computers connecting to a server, the firewalls themselves negotiate a secure link to bridge the two entire sites together.

What is Firewall Configuration and Why is it Important? - Fortinet