This object is a bitmap list of ports on the OSPF-enabled VLAN, and its description explains that a passive OSPF interface will not send out routing updates even though it may still be part of the network. An administrator uses this list to mark specific ports as passive, useful for connecting to end-host segments where you want the subnet advertised but don't want to risk forming stray adjacencies. Including a particular port in this list would stop the OSPF interface from transmitting hello or update packets out through that port while keeping the interface's network reachable in the routing table.