A dongle is a small piece of hardware that attaches to a computer, TV, or other electronic device in order to enable additional functions such as copy protection, audio, video, games, data, or other services. These services are available only when the dongle is attached.
"Attached" does not need to involve a wired connection. The dongle may communicate wirelessly with the device it enables via NFC, for example.
The term "dongle" originally addressed a software protection device. The construct is now more broadly used especially for
原文：http://www.cnblogs.com/SZLLQ2000/p/5120312.html