Interface Groups can contain rules that apply to multiple interface at once. Rules applied to groups only affect current group members, so when an interface is removed from a group, rules for that group no longer apply.
In pfSense® software, interface groups can be managed from the list view at Interfaces > (assign), on the Interface Groups tab.
Group Name is the name of the group as it will appear in the GUI, such as on firewall rule tabs.
Description is a longer description for reference
Member(s) is the list of interfaces that belong to the group. To add new members, click then pick the interface for this group from the list and repeat that process for additional group members. Click to remove a member from the group.
Rules for Interface Groups are processed after Floating rules, but before interface tab rules. See Firewall Rule Processing Order
Using Interface Groups for WANs will not put “reply-to” on the resulting pass rules because it can’t do so for rules in groups. Due to this, traffic that enters via an alternate WAN (non-default route) and is allowed by pass rules on an interface group will exit back via the default route. This only applies to rules that pass traffic, blocking is fine either way.
To keep the proper return routing, place pass rules for inbound services behind the firewall on their respective WAN tabs, and not on the group tab.