Dongle

Dongle (pronounced dong-guhl)

(1) Historically, a hardware device attached to a computer without which a particular software program will not run; used to prevent unauthorized use.

(2) Latterly, a device (almost always plugged into a USB port) to enable connectivity with other devices, peripherals or networks.

(3) In (very) casual use, any small USB device. 

1980: First recorded in 1980, shortly after the debut of the original IBM PC-1 and although often cited as arbitrary coinage, is possibly derived from dangle, given the first dongles dangled from a short cable.  Unfortunately, the advertisement in a computer magazine in the early 1990s which claimed the dongle was invented by an engineer named Don Gall was just an attempt to make nerds laugh and maybe create an urban legend.

Parallel-port dongle.

Historically, a dongle was a small (about the size of a box of matches) pass-through device, a piece of hardware which connected to a PC’s 25-pin parallel (then used most often for a printer) port.  It provided usually a form of copy protection and license enforcement in that the software with which it was supplied wouldn’t run unless dongle was plugged-in.  Most PCs had only one printer port (although from the original IBM PC-1, there was always support for three physical ports) but it was possible to daisy-chain multiple dongles on the one port and still connect the actual printer (as the last device in the chain).  The parallel dongles were famously robust and reliable but less successful were the early implementations of dongles as USB devices; problems not solved until the early 2000s.

Raspberry Pi Nano WiFi dongle.

Dongle has also come to mean just about anything small which connects to a USB port and does something.  Although the definitions were never codified, the convention of use with USB devices seems to be that a dongle is something which in some way is an enabling device for something else (such as connecting to a WAN, LAN, Wi-Fi or a streaming feed) whereas “stick”, “pen-drive” or “key” is used for something self-contained such as a flash drive.

Rainbow Technologies' "Don Gale" dongle advertisement (1992).  While there was no actual Mr Gale, the story related is exactly the reason the software protection hardware was created.