Facebookon ha az elküldött leveleim melett egy fekete nyil van, az azt jelenti hogy a címzett még nem olvasta el?

The arrows mean you were the last one to say something in the message thread. If there have been multiple replies, the arrow indicates that it is not your "turn" to say something. If there have not been any responses, it means you were the first to speak and have not gotten anything back yet. Hope this helps. :) - a Facebook-ról

Röviden azt jelenti, hogy még nem válaszoltak az üzenetedre.