Definition of vlan?

A VLAN is a group of PCs, servers and other network resources that behave as if they were connected to a single, network segment — even though they may not be. The resources and servers of other users in the colocation facility will be invisible to each of the other VLAN members. Equally important, VLANs help meet performance needs by segmenting the network more effectively. Unlike standard switching, they restrict the dissemination of broadcast as well as node-to-node traffic, so the burden of extraneous traffic is reduced throughout the network. Security can also be improved. Since all packets traveling between VLANs may also pass through a router, standard router-based security measures can be implemented to restrict access as needed.