HLR = Home Location Register

Home Location Register, shortened as HLR refers to a database

“The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There can be several logical, and physical, HLRs per public land mobile network (PLMN), though one international mobile subscriber identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at a time.”

Learn More Here: https://en.wikipedia.org/wiki/Network_switching_subsystem#Home_location_register_.28HLR.29