A BLE beacon broadcasts its identity to nearby Bluetooth devices, to enable the other devices to determine their location relative to the beacon, and to perform actions based on information broadcast by the beacon.
Example applications of beacons include indoor positioning system, location-based advertising and more.
From the definition of its purpose as a broadcast device, a BLE beacon thus cannot be connected to, and can only send information in its Bluetooth advertisement packets.
There are several BLE beacon protocols. The Ameba BLEBeacon library supports the iBeacon and AltBeacon protocols.