What is this?

Not sure what bike you have , small Din , on my gs hex , l use it for trickle charger, but can be used as a power source 🤙😎

It is the equivalent to a cigarette lighter style plug. Except it is DIN style (also called a Hella or Powerlet style). You can buy an adapter to convert it to a USB port to charge your phone etc.

Longtime Harley rider, now a BMW owner. Few things are different. Thx.

I like it much more then standard cigarette lighter socket. On my previous bikes, I had classic cigarette lighter socket to power up my GPS and on every one of them, on longer rides the plug would work its way out of the socket.
On my GS I use this DIN socket to power my Garmin GPS. The DIN plug has never worked its way out of the DIN socket.

The BMW auxiliary ports (DIN) are generally limited to 5 Amps, so not a good option for heated gear or compressor.