OPT

From PFSenseDocs

Short for Optional, used to describe interfaces other than LAN and WAN. These can be Ethernet or wireless interfaces, just like LAN and WAN. Additional networks can be added using OPT interfaces. Common uses include multiple LAN's, DMZ segments, contractor or vendor segments, and wireless access points.

OPT interfaces can be set to DHCP or static IP with gateway to function as additional WAN connections, referred to as OPT WAN interfaces.