Bluetooth is one means by which electronic devices communicate wirelessly with each other. Many tablets have WiFi, but Bluetooth is less common, especially with children’s tablets (and Near Field Communication is even more rare).
The nabi 2S does have Bluetooth 4.0 built in. This means that the tablet can use Bluetooth to connect to other devices, such as speakers, computers and headphones. Whilst Bluetooth isn’t as good for data transfer as WiFi, or direct connection, it is very useful for connecting to such as speakers.
The Bluetooth can be turned off, if it isn’t needed, which is useful as otherwise it can cause an unneeded drain on the tablet’s battery.