The Dongle is a Lightning® to 3.5 mm Headphone Jack Adapter cable for use with the iPhone/iPad/iPod
Keep Your Headphone Jack
The Dongle allows you to continue to use your wired earphones or headphones and aux cords with your Apple® devices.
*What's a Dongle?
A dongle is the band-aid of hardware. It's meant to make up for gaps in functionality or to add functionality.
The audio adapter cable that came with your phone is considered a dongle. The audio adapter dongle allows wired headphones to still be used. It does this by converting the 3.5 mm plug (found on the end of a headphone wire) into a Lightning® connector that can plug into a phone.