InBluetooth, all devices and modules are identified by a globally unique address. This is inserted into the Bluetooth module by the manufacturer and ensures that the Bluetooth devices can be identified without any doubt.
Since the complete Bluetooth frame is structured in little-endian format, the most significant bits ( MSB) are also at the end of the 48-bit Bluetooth address. The 24-bit Lower Address Part( LAP) sent at the beginning forms the essential part of the Bluetooth address together with the middle 8 bits of the address, the Upper Address Part (UAP). This means that already '2^32' different addresses can be generated from the 32 available address bits. The remaining 16 address bits are called Nonsignificant Address Part( NAP).
There are two Bluetooth addresses for power saving modes. The Active Member Address( AMA), which is used for both hold mode and park mode, and another one, the Passive Member Address( PMA), which replaces the Active Member Address in park mode.