Geofencing is the practice of triggering an action when a device enters or leaves a mapped area. It is location based and coarse, good for area context but not for resolving who is nearest.
The longer version
Geofencing puts geofences to work. An app watches a device's location and acts when it crosses into or out of a defined area: opening a screen, sending a message, logging an arrival. It relies on the phone knowing roughly where it is, usually through satellite or network location.
The approach is coarse by design. It can tell that a device is inside a region, which is enough for reminders and rough context. It cannot tell which specific provider a person is beside, because everyone inside the same fence registers the same way.
Signal based proximity answers the finer question. Rather than checking a map boundary, it senses a provider's short range broadcast and resolves the single nearest pairing on a server. Geofencing can set the stage by narrowing the area, and proximity can settle the exact match inside it.
The Parousya method
Geofencing knows a device is inside an area. The Parousya method goes further, sensing a short range signal to identify the single nearest provider, which is the resolution a coarse boundary cannot provide.