Unique Property Reference Number

The Unique Property Reference Number (UPRN) is a unique number (a geocode) for every addressable location—e.g., a building, a bus stop, a post box, a feature in the landscape, or a defibrillator—in Great Britain. Over 42 million locations have UPRNs, which can be found in Ordnance Survey's AddressBase databases.

Source: Wikipedia — Unique Property Reference Number (CC BY-SA 4.0)