On this day, 24 deities were born in the outlands, the true neutral plane that brings balance to the outer planes.
Each deity received reign over one of the 26 planes, excluding the material plane, which was to be ruled over by mortals, and the ethereal and astral planes, that were created by the Lady of Worlds.
The most powerful deities at that time were the four that reigned over the elemental planes.
Those that reign over the para-elemental planes are called lesser deities, those that reign over the outer planes are called either upper or lower deities, depending on if they are a Celestial or a Fiend.