Faas means Firewall as a Service. You can use the firewall as a hardware appliance (physical computer in your network), as a virtual appliance (still a computer, but it’s running in the cloud), or you can pay for a firewall as a service. It means you are not responsible for the firewall itself. Instead, your provider is making sure it’s running and secure; you are just specifying what it should be doing. An example is Azure Firewall.