The Source was a cosmic entity responsible for the creation of the New Gods. Highfather, the leader of New Genesis, was capable of consulting the Source, and would do so on matters of great importance, such as a possible war with Darkseid of Apokolips.
In the DC comics, the Source is literally the source of all life in the universe, and is responsible for the "god wave" which created the Old and New Gods, as well as other deities such as the Norse and Greek Gods.
During Countdown to Final Crisis, the Source initiated the extinction of the New Gods as a means to create a fifth-world, using the Infinity-Man to kill New Gods such as Granny Goodness, Mister Miracle, Orion, Big Barda, and finally Darkseid himself. However, Darkseid and his minions have recently resurfaced on Earth.