Akh is a term used to describe the spiritual essence of a person and the first of three components that make a complete person - the other two being Ba and Ka. Upon death, the akh is the first component to enter afterlife.
According to traditional lore of the Followers of Set, a Setite's akh departs to the afterlife when a sire shares the dark water of the river that flows between worlds with her childe. This provides the Serpent with a foothold in both the living world and Duat.
- Players Guide to Low Clans, p. 24