basically its a connection between devices. wireless. like infrared but 10x better!

Bluetooth lets phones with bluetooth work with other bluetooth stuff like wireless headsets, other phones and even cars.

Even more simply put.... It connects stuff...

bluetooth first started off as military technology

Bluetooth is a standard developed by a group of electronics manufacturers that allows any sort of electronic equipment -- from computers and cell phones to keyboards and headphones -- to make its own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a standard that works at two levels:
It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.
It also provides agreement at the next level up, where products have to agree on when bits are sent, how many will be sent at a time and how the parties in a conversation can be sure that the message received is the same as the message sent.

I hope thats easy enough

please explain easily.