The only thing i can think here is if they are talking about Private VLAN's.
From Cisco-Online:PVLANs provide layer 2 isolation between ports within the same broadcast domain. There are three types of PVLAN ports:* Promiscuous? A promiscuous port can communicate with all interfaces, including the isolated and community ports within a PVLAN.* Isolated? An isolated port has complete Layer 2 separation from the other ports within the same PVLAN, but not from the promiscuous ports. PVLANs block all traffic to isolated ports except traffic from promiscuous ports. Traffic from isolated port is forwarded only to promiscuous ports.* Community? Community ports communicate among themselves and with their promiscuous ports. These interfaces are separated at Layer 2 from all other interfaces in other communities or isolated ports within their PVLAN.For Example: If you host several servers from different companies, you can be sure that there will be no communication between the servers although they are in the same subnet. Communication is only allowed from the rules above mentioned.