Answer Description

Wikipedia

A geofence is a virtual perimeter for a real-world geographic area. A geofence can be dynamically generated (as in a radius around a point location) or match a predefined set of boundaries (such as school zones or neighborhood boundaries). The use of a geofence is called geofencing, and one example of use involves a location-aware device of a location-based service (LBS) user entering or exiting a geofence. Geofencing approach is based on the observation that users move from one place to another and then stay at that place for a while. This method combines awareness of the user's current location with awareness of the user's proximity to locations that may be of interest. This activity could trigger an alert to the device's user as well as messaging to the geofence operator. This info, which could contain the location of the device, could be sent to a mobile telephone or an email account.