A virtual LAN (VLAN) is any broadcast domain that is partitioned and isolated from a hospital network at the data link layer (OSI layer 2). Essentially, you're taking a switch and partitioning it (e.g. similiar to hard drive) into multiple, seperate LANs. LAN is an abbreviation of local area network.
To subdivide a network into virtual LANs, one configures a medical device to more than one network switch or router.