Djed was the oldest symbol of the four pillars of Osiris and had a deep religious meaning to the Egyptians.
The late form as an ugly fat man(?) with four pillars upon his head was not an Egyptian style, but an imported Asiatic way of depiction. Djed-pillars are known from the second dynasty and it's possible that Osiris originally was shown in this way before he appeared with a human body in dynasty five. The pillars may show a bundle of papyrus stalks tied together or possibly a part of the human spine.
Among other things they stood for stability and continuity. In the pyramid texts they were equal to divine powers and Ptah's staff was partly made of them. In one version of the Myth of Osiris Djed was transformed into lumber and in reliefs made during dynasty 18 the king is shown erecting four wooden pillars.
Main text