sbellon> packet filter (that's what it is, it is no firewall)
I'd have called it a packet filtering firewall or a network level firewall. It examines the header of each network packet in turn and decides on the rules given whether to block or allow the packet.
The alternative is a proxy server firewall (aka application level firewall). All requests for access are processed at the firewall so that all packets are sent to and from the firewall, rather than from the hosts behind the firewall. This type of firewall inspects not only the packet header but the content as well. As you can imagine, it is also a lot more expensive in terms of computer resources.