Bluetooth Device Address (or BD_ADDR) is a unique 48-bit identifier assigned to each Bluetooth device by the manufacturer.
Bluetooth Address is usually displayed as 6 bytes written in hexadecimal and separated by colons (example - 00:11:22:33:FF:EE).
The upper half of a Bluetooth Address (most-significant 24 bits) is so called Organizationally Unique Identifier (OUI). It can be used to determine the manufacturer of a device (Bluetooth MAC Address Lookup form).
Additionaly to identification, Bluetooth Device Address is used to determine the frequency hopping pattern in radio communication between Bluetooth devices.