VLR (visitor location register)

A network database that holds information about roaming wireless customers. (Cingular)

Visitor Location Register (VLR) is a database - part of the GSM mobile phone system - which stores information about all the mobiles that are currently under the jurisdiction of the MSC (Mobile Switching Center) to which it is attached. Of all the information it stores about MS (Mobile Station), the most important is LAI (Location Area Identity). LAI identifies under which BSC (Base Station Controller) is the MS currently present. This information is very vital in call set up process.

Whenever MSC detects a new MS in its network, in addition to creating a new record in VLR, it also updates the HLR of the mobile subscriber apprising it about the new location of MS.

(Wikipedia)