It's a wireless communication protocol for connecting devices through the air - it's slower than Wi-Fi but is often simpler to set up, and is usually preferred for device-to-device transfers.
Mice, keyboards, smartphones, printers, hands-free car kits, laptops and more followed suit, as did successive versions of the Bluetooth standard.
The characteristics of Bluetooth
Bluetooth is designed to be as easy to use as possible which means a lot of the technical aspects of the technology are hidden away from users - at most you'll have to enter a PIN code when you're trying to get two devices to sync up together.
Bluetooth BR/EDR is more limited in terms of range but is more suitable for keeping up a continuous connection for streaming audio, for example .
Bluetooth is simpler to set up and doesn't use up much power but has a shorter range and is slower - binge watching Netflix is usually out of the question.
Despite its illustrious history, the best days of Bluetooth may still be ahead of it.