PVID represents the primary vlan id, in other words if a packet doesn't have a vlan tag, which vlan does it belong to? The ethernet driver handles this rather trivially, in the case of vlan0ports="1 2 3 4 5*", ports 1-4 are set to PVID 0 (vlan0). Since the wrt needs to recieve packets from both the LAN (vlan0) and the WAN (vlan1), port 5 is a special case appearing in both vlan0ports and vlan1ports. This is where the '*' is used -- it determines the PVID of port 5, which is also the only port not to untag packets (for hopefully obvious reasons).