What is vlan? what is the command to create vlan?

A VLAN is a group of end stations in a switched network that is logically segmented by function, project team, or application, without regard to the physical locations of the users. VLANs have the same attributes as physical LANs, but you can group end stations even if they are not physically located on the same LAN segment.Any port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered a logical network. Packets destined for stations that do not belong to the VLAN must be forwarded through a router.

switch# configure terminal switch(config)# vlan 5switch(config-vlan)# name accountingswitch(config-vlan)# state activeswitch(config-vlan)# no shutdown