Diachaim is the name of divine energy, used freely by the Gods and through Them by Priests and Templars. After the Godsdeath War, Diachaim remained in Imperian and allowed entities to form and grow. Diachaim which has pooled in the physical realm and become disconnected from its spiritual counterpart is known as magick.
`Contrary to the theories of a few scholars, the universe is not an empty void. Just as oceans are filled with water, creation is filled with the Diachaim. Invisible but as real as any other resource, it flows through and around everything. In some places the flows are thinner, and in others it collects and pools around certain objects. Just like an ocean, it has flowing tides and currents, some ripping through reality like a raging storm, others lapping gently at its edges.
It is this power that the Gods use to manipulate all things. Pure and untainted, the Gods can draw on this power in their omnipotent intelligence, manipulate it, and use it to do nearly anything. Some mortals call upon this power through the Gods, who grant their power to their followers in the form of devotion. In some cases, mortals deemed unworthy have been denied devotional powers by the Gods, but this is rare indeed.
— From a scroll describing the nature of Diachaim in the Third Age