system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is Geofencing?

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gpt
The wikipedia page explains this well :

>A geo-fence is a virtual perimeter for a real-world geographic area.[1] A geo-fence could be dynamically generated—as in a radius around a point location, or a geo-fence can be a predefined set of boundaries (such as school zones or neighborhood boundaries).

>The use of a geo-fence is called geo-fencing, and one example of usage involves a location-aware device of a location-based service (LBS) user entering or exiting a geo-fence. This activity could trigger an alert to the device's user as well as messaging to the geo-fence operator. This info, which could contain the location of the device, could be sent to a mobile telephone or an email account.

So, basically, a geo-fence is when instead of installing a real fence, you program a computer to tell you if you're inside or outside the fence.