Connecting Devices using Bluetooth
Bluetooth is a wireless connection that is used to link two devices together. These can be complimentary devices like a smartphone and Bluetooth Headphones, or a laptop and a printer, or it can be two devices that you wish to share data over for example two smartphones or a PC and a Tablet.
You can link multiple devices together for example a laptop to a printer , a digital radio, a set of headphones and a wireless mouse. On each occasion you "pair" the two devices together.
Bluetooth is essentially a networking standard. It is popular because it is wireless, inexpensive and automatic - the user doesn't have to enter any settings beyond saying 'yes go ahead and connect'. It creates a personal area network (PAN) (There's more on network types here)
Bluetooth transmits data via low power radio waves on a frequency around 2.45 Ghz. It actually switches frequencies 1600 times per second to avoid any two devices being on the exact same frequency at the same time.
Since 2009 there have been two types of Bluetooth. The classic Bluetooth and Bluetooth Low Energy (BLE). BLE does the same as Classic except it uses a lot less power making it ideal for portable devices. The video explains more on this.
Discusses Bluetooth Low Energy