Dongle
A physical key you plugged in to let the program start — copy protection's hardware variant.
A dongle sat in the parallel, serial or later USB port, and the protected software refused to run unless it recognised the chip answering there. The idea was simple: a file can be copied, a piece of hardware can't. Expensive professional software — CAD, music studios, industrial control — clung to the model long after it turned impractical for consumers.
The scene answered as usual. Where a nibbler or X-Copy dealt with protected disks, crackers wrote "dongle emulators" or simply patched the check out entirely, much as a keygen did with serial numbers. What was left was the headache for the legitimate customers who lost the key and were stranded without the software they had paid for.