This is a bitmap (PortList) reporting which ports are currently, operationally acting as isolated host ports within a private VLAN's primary/secondary association, meaning they can reach the promiscuous port but not each other. An administrator checks this to verify which ports the switch has actually placed in the restricted host role, which is the mechanism used to keep end-user ports from seeing each other's traffic while still reaching a shared gateway. For example, in that same hotel-room scenario, this list would show the individual guest-room switch ports that are isolated from one another.