Primal Deities are the ancient deities who it is believed created the gods (or the younger gods as they are called when in reference to these ancient deities).
Their worship is now all but forgotten. They are Ashra, Vuh and Elim. It is believed they came from the Primal Chaos. Some very ancient civilisations believed that preceding even the Primal Deities was their creator Arn. Some scholars believe that Time is a fourth Primal Deity.
See the chart below for the interrelationship with each other and with the younger gods.