WAN needed or just like any other Ethernet-Interface

[janw.zc]

Hello,
I'm quite new to OpnSense and would just like to know, if the WAN Interface had any special characteristic or if it was an interface just like any other interfaces as well? Right now we have 3 local interfaces on the virtualk OpnSense machine and use it as Firewall/Router but soon we would like to route or WAN-Traffic through the firewall, can I simply use a normal LAN-Interface?

Thanks a lot in advance,

janw