VLAN stands for Virtual Local Area Network. Any collection of computers connected together and communicating with each other is called a network. When the number of computers on a network becomes too high, the amount of traffic becomes problematic. Breaking the network into Virtual networks solves this problem. On Taylor's network, a switch sits between each virtual network. The switch acts as a filter which monitors all activity and passes only the traffic destined for PCs sitting behind the switch.
PCs in one VLAN can be isolated from PCs in another VLAN using Access Control Lists. Faculty/Staff servers, for example, are not accessible from student VLANs. ACLs are maintained by the Security Analyst.