The full form of HLR is Home Location Register

Home Location Register (HLR) is a database that contains data regarding authorized subscribers using a global system for mobile communication (GSM) core network. The home location register stores information ranging from phone numbers to current location of the subscriber. Some data contained in the home location register include the mobile Station International Subscriber Directory Number (MSISDN) which is a list of the telephone numbers used by the subscriber and the International Mobile Subscriber Identity (IMSI) which is a unique identifier of each subscriber identity module (SIM) and is the primary key for each HLR record of each subscriber.

Cell phones and their corresponding SIMs are mostly on the move. The HLR is used to identify their last known location. This information is updated each time the device is transferred in to another location. The HLR also facilitates Short message services (SMS) by scanning through the HLR to identify the mobile switching center (MSC) currently used by the receiving party. If the recipient is reported as not available by the receiving MSC, a message waiting flag is sent on the HLR. The message is then delivered once the recipient is located on any MSC.

Other mobile components associated with the HLR include the gateway mobile switching center (G-MSC), the authentication center (AUC) and the visitor location register (VLR).