Bluetooth Beacons support is a new addition to iOS 7.
Rather than using GPS, it works by determining the phone's location relevant to a Bluetooth beacon. These beacons constantly broadcast a UUID that identifies them. Beacons offer more accuracy indoors as GPS doesn't work that well in covered spaces.
The standard CoreLocation framework defines a new class called CLBeaconRegion:
A CLBeaconRegion object defines a type of region that is based on the device’s proximity to a Bluetooth beacon, as opposed to a geographic location. A beacon region looks for devices whose identifying information matches the information you provide. When that device comes in range, the region triggers the delivery of an appropriate notification.
An apps can request to be informed when they are near these beacons. This is how the MLB app works. It is programmed to recognize these beacons and to provide the user with offers and information based on location.
In addition to support within apps, Passkit also provides the support these beacons. It works in roughly the same way. The pkpass file contains a list of UUIDs that identify various beacons and when the phone is near a beacon, the pass is shown on the lock screen.
You can read more about Passkit's support by looking at the package format guide
Hopefully that answers your question.