Dongles & adaptors
A dongle is a small physical device that connects to a computer port, either to provide an additional function, or to allow signal conversion.
There are many different uses for dongles. For example:
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a security key that provides authentication that is external to the computer (such as a personal license)
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an adaptor that lets you plug a cable of the “wrong” type into a different kind of connection1 (an Ethernet to USB C converter, for example, or an HDMI-to-VGA adaptor)
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a dongle that provides wireless connection, such as that needed by a Bluetooth mouse or keyboard, or to WiFi
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a means of transforming signals or data by sitting between the port and the external device, such as gaming cheat codes or network packet sniffers
Adaptors with multiple ports
It’s possible for an adaptor to accept more than one connection at the same time. This example shows a multiport adaptor that lets you connect three things — a USB Type-C charging cable, an HDMI display, and a USB-A device — into a single USB-C port.
1 Even simple adaptors might be more sophisticated than you realise. An adaptor is almost never simply joining matching pins (wires) together. It may often contain embedded software that converts between the different protocols in order to make the signals they pass through make sense. Be careful: adaptors are easy to lose or forget because they are small... but that internal complexity means they are sometimes surprisingly expensive!