- "We've only been here for a couple of days. This stuff is pretty old. It's that, or there really are ghosts."
- ―Dr. Rodney McKay[src]
A ghost is the soul or spirit of a deceased person, taken to be capable of appearing in visible form or otherwise manifesting itself to the living. Descriptions of the apparition of ghosts vary widely: the mode of manifestation can range from an invisible presence to translucent or wispy shapes, to realistic, lifelike visions. Many of the Athosians believed the spirits of the Ancestors inhabited Atlantis. (SGA: "Hide and Seek")