The Adeptus Mechanicus is the official Imperial name within the Adeptus Terra for the Cult Mechanicus or Cult of the Machine. The Mechanicus acknowledge the Emperor of Mankind as the ruler of the Imperium, but not the religious truth of the Imperial Cult or the Ecclesiarchy. Instead, the Mechanicus follows its own dark and mysterious scriptures and worships the deity they call the Machine God or the "Omnissiah."
Forge World Graia is one of their Forge Worlds, located in the Segmentum Tempestus.