A ghost is the footprint of a magical being's soul. When a person holds resentment, fears, or simply a strong connection somewhere, they will continue to linger on in the world through this imprint. It can be assumed that once a being becomes a ghost, this cannot be undone, nor can ghosts be destroyed (although they can be repelled by certain magics, such as Lumos and Skurge). Souls that have been ripped apart or damaged by cursed magic will be unable to become ghosts. Some magical creature abilities can still impact a ghost, such as a Basilisk's gaze, but as a ghost cannot die again, it will simply be petrified until restored.

Ghosts float weightlessly around in any direction they wish, bearing the appearance they held at the time of their death, but with a translucent grey-silvery hue about them. They will also hold onto any knowledge and emotions they had at the time of their death, being unable to move on from strong resentment, for example. As ghosts are not physical beings, they cannot hold or touch items or living people. It is said if a ghost passes through a person, it feels like being submerged in an ice bath. They can also cause disturbances in the atmosphere, with flames and other elements. Certain ghosts will randomly leave a substance called ectoplasm behind.

Ghosts tend to return to the place they die upon becoming a ghost, but the Spirit Division can control or even bind a ghost to restrict it to a certain space, if needed. Although Muggles cannot see ghosts, they may still experience the atmosphere changing and what they would call paranormal activity. Certain animals can also return as a ghost, but it isn't known whether these need to be magical creatures or if all animals could have this potential.