Dongle

A dongle is a small piece of computer hardware. when you plug the dongle to your device, it will provide additional functionality, or enable a pass-through to such a device that adds functionality.
The term has since been added to other types of devices with a similar form factor, such as:
Examples.
Security dongles are typically used to help prevent unauthorized use and copying of certain forms of software. Initially using ports such as the serial port or parallel port, most are now in USB format.
Very short cables that connect relatively large jacks to smaller plugs/. It allow cables to be easily installed and removed from equipment with limited space available for connectors. The Chromecast devit negates the need for a short adapter cable.