Luz (Hebrew: 'לוז') is the name of a small bone in the human body, at the top of the spinal column (the seventh cervical vertebra) or at the base of the spinal column (the coccyx), according to different traditions. Muslims and Jews believe that this is the bone from which the body will be rebuilt at the time of resurrection, and share the belief that this bone does not decay. Arabic books refer to this bone as "'ajbu adh-dhanab" --(عَجْبُ الذَّنَب).
There is an aggadah (legend) in the midrash that the Roman Emperor Hadrian asked how man would be revived in the world to come, and Rabbi Joshua Ben Hananiah replied that it would be "From Luz, in the back-bone." "Prove this to me," said Hadrian. Then the Rabbi took Luz, a small bone of the spine, and immersed it in water, but it was not softened; he put it into the fire, but it was not consumed; he put it into a mill, but it could not be pounded; he placed it upon an anvil and struck it with a hammer, but the anvil split and the hammer was broken. (Ecclesiastes Rabbah xii / Genesis Rabbah xviii).
- Sefer Ta'amei Haminhagim. 425.