NFC, i.e. "Near Field Communication", is turned on.
If you are using a phone payment system, or one of those features that allows you to share media between 2 (very) nearby devices, then NFC is what they use. It can also be used for authentication (e.g. unlocking doors), and various other tasks. If you don't do any of that stuff (I don't myself) then you can turn it off and the icon will go away.