Definition
HLR (Home Location Register)
The carrier database of mobile subscribers that an HLR lookup queries to check a number's live status.
The Home Location Register records whether a SIM is active, which network a number belongs to, and whether the handset is currently reachable. An HLR lookup is a passive signaling query against it — no call or SMS is sent.
HLR data is mobile-only. It doesn't cover landlines or classify VoIP, so it's a component of liveliness rather than a substitute for it.