Bluetooth is a way for gadgets like tablet computers to connect to other equipment over a short distance. Bluetooth creates a private, highly secure short range network that allows for cable free and easy connection. It's possible to connect more than one device through Bluetooth at a time. An example benefit would be if your mobile phone and your laptop support bluetooth, you could send pictures from your phone to your laptop without the need for a usb cable. Less cables are always a good thing in our book. The Sony Tablet S supports bluetooth.
This is the best place to start if you'd like to learn more about Bluetooth:
More on Bluetooth at Wikipedia
There's also a good guide on Which to do with all things 3G, Wi-fi and Bluetooth.
