What is the definition of a "firewall"?
And it doesn't really matter. You can call it "alksjfaliskdfgh" if you wish. The fact is, NAT adds a security barrier that is incredibly effective in practice.
But it really doesn't. If you turned off NAT your computers would have the exact same security as they do with NAT.
But it really doesn't. If you turned off NAT your computers would have the exact same security as they do with NAT.