What?
Bluetooth is a wireless technology standard for exchanging data over short distances(using short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz[4 from fixed and mobile devices and building personal area networks(PANs Invented by telecom vendor Ericsson in 1994[5 it was originally conceived as a wireless alternative to RS-232RS-232 data cables It can connect up to seven devices overcoming problems that older technologies had when attempting to connect to each other
How?
A Bluetooth device uses radio waves instead of wires or cables to connect to a phone or computer. A Bluetooth product, like a headset or watch, contains a tiny computer chip with a Bluetooth radio and software that makes it easy to connect. When two Bluetooth devices want to talk to each other, they need to pair. Communication between Bluetooth devices happens over short-range, ad hoc networks known as piconets. A piconet is a network of devices connected using Bluetooth technology. When a network is established, one device takes the role of the master while all the other devices act as slaves. Piconets are established dynamically and automatically as Bluetooth devices enter and leave radio proximity.
 | Bluetooth Data and File transfer using Arduino.pdf |