A copy protection device.
When buying some expensive software you may be given a hardware 'dongle'. It looks a bit like a memory stick.
The dongle contains an encryption key that allows the software it is protecting to run.
You plug the dongle into a suitable port (USB, Parallel port etc). If the software cannot find the dongle then it will not run.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: Dongle