The ba was the part of the ancient Egyptian soul depicted as a human-headed bird. Egyptians imagined it as a mobile aspect of a person that could travel between the tomb, the afterlife, and the world of the living after death.
The ba was not the entire soul. It was one element in a larger Egyptian view of identity that also included the ka, a vital force or spiritual double; the akh, a transformed and effective spirit; and the sheut, or shadow. Egyptian funerary rituals and spells were intended to help these aspects function together safely after death.
Artists commonly showed the ba with a human head because it represented the deceased person's personality and agency. It was often pictured visiting the mummy or tomb, sometimes perched near the body. This imagery explains why the ba is frequently confused with the ka: the ka was also essential to continued existence, but it was not normally represented as the human-headed bird.
After death, the ba was expected to unite with the ka and become part of the akh, enabling the deceased to live effectively in the afterlife. These ideas changed over time, but the human-headed bird remains the standard visual symbol of the ba.