NFC is on (Near Field Communication). I have tested it between my ONE and wife's LG G2 and it works fine for transferring a picture from phone to phone or what have you. It's a bit tricky to use with the ONE though. You can't place it exactly back to back due to antenna placement in the device. You need to position the ONE about halfway down the back of the other phone and it will connect nicely.
If you don't want to use it simply go to Settings>More and uncheck the NFC box and the icon will go away.