The Nejeter Tablet is a stone stele that acts as a decipher to the map that would lead to the tomb of Akhenaten. By deciphering the code, it would give valuable information to the royal tombs in the area, including that of Akhenaten and Ramses the Second.
When Nimrod visited Hussein Hussaout, he hinted that he had this ancient tablet, but was weary of using it because of dangerous forces that may take advantage like the Ifrit. It is later revealed that it was part of a fascade for Hussein to bind Nimrod with a djinn seal without anyone detecting him.