Bluetooth is a wireless technology standard. It provides a way to exchange data over short distances using short-wavelength radio transmissions in the band 2,400 to 2,480 MHz.
It allows to create PANs (Personal Area Networks) with the "correct" level of security. It is implemented on various types of devices such as computers, smartphones, sound systems that can read digital audio from a remote source, and so on.
Arduino BT board natively implements this technology. It is now supplied with ATmega328 and a Bluegiga WT11 Bluetooth module. The reference page is
In my opinion, the best way to proceed in many projects is to keep a general purpose board at the core of our designs ...