A dongle is a special USB stick. I have a dongle that enables me to use my Pfaff 5D software on my computer. If I don't have it 'plugged into' my computer, the software won't work. I suspect Pfaff developed it to prevent the software from being copied and used by more than one consumer. I can install the software on more than 1 computer, but I can only use it on one at a time, because I have only 1 dongle.