This displays if you're missing gem or enchants from any of your gear or if you currently have a very low iLvl item equipped in a small, concise area on your screen.
You can set the iLvl minimums in the Custom Options tab.
Original by Xpariah: https://wago.io/Hkacqsn7-
Fan Update by Alf: https://wago.io/B119bPwq7