Ghost


 * For the audio drama, see Ghosts (audio).

Ghosts are a phenomenon occurring in the collective mythology and popular culture of Earth and other worlds including, perhaps, Skaro. Those who believe in ghosts sometimes hold them to be souls that could not find rest after death, and so linger on in the world of the living. This inability to find rest is often explained as unfinished business.

Doctor Who
A ghost is sometimes referred to as a fetch, and the woods around Fetch Priory were long believed to be haunted, the result of its being near a relative continual displacement zone or hole in time leaking images and other phenomena from light years away (DW: Image of the Fendahl)

Light was an extraterrestrial being who sought to catalog all life in the cosmos. Shortly after completing the task he went into hibernation within Victorian Perivale, a house being built around his ship as he rested. When he awoke he was outraged that evolution had rendered his findings useless and terrified the house pulling apart the guests to see what makes them tick. Ultimately he discovered that he himself had undergone change and departed to the stars finally seeing the error of his ways. He was a transparent ghost-like being whose appearance depended on his surroundings and he could do a multitude of things just like a phantom (DW: Ghost Light)

The Ninth Doctor later matched this explanation while fighting the Gelth (DW: The Unquiet Dead)

The Doctor explained that Psychic residue was a cause of ghost sightings. (DW: The Pandorica Opens)

Torchwood
The Quantum transducer was an extradimensional artifact that amplified residual hauntings into intricate visions. These ghosts are explained as psychic residue from powerful emotional events, bits of people from years before just hanging around. Thus the transducer was dubbed the "Ghost Machine". (TW: Ghost Machine)

Eugene Jones was able to interact with Gwen Cooper of Torchwood Three for a time after his death as a de facto ghost. Ultimately, he briefly became visible to not only Cooper, but other members of the Torchwood team, before "crossing over" and ceasing to be a ghost. This was due to his consumption of a Dogon Sixth Eye beforehand granting him a new perspective on life. He would eventually unlock the secret to true peace and happiness allowing him to let go of his past life and surrender to death's advances (TW: Random Shoes)

A Cardiff building was haunted by three cowled men with scythes, it is unknown what these things actually are, but they were considered ghosts. Toshiko Sato and Ianto Jones were sent by Torchwood Three to kill them. They appeared in front of them, and were shot dead by Tosh and Ianto. They were merely "shadows" cast by The Rift. (TW: Exit Wounds)

The Sarah Jane Adventures
Sarah Jane explained that events get recorded on their surroundings and under certain circumstances can get played back again (SJA: Eye of the Gorgon)

The "ghosts" encountered at Ashenhill Manor were nothing of the sort, they were helpless innocents who had been trapped inbetween the dimensions by Erasmus Darkening's malfunctioning equipment. (SJA: The Eternity Trap)

When Sarah Jane was sent back in time to collect a fragment of Chronosteel she encountered a ripple from the future, echoes of a traumatic moment that had yet to happen. Thankfully her actions helped to prevent this horrible event from ever seeing the light of day. (SJA: Lost in Time)

K-9
Professor Alistair Gryffen's numerous failed attempts to retrieve his family with The Space-Time Manipulator eventually began to take their toll on the continuum, warping reality into the shapes of his wife and children. They functioned as de facto ghosts, needing to trade places with Jorjie and Darius so they could take physical form and even going so far as to restore The Professor to his default setting, as he was before he lost them. They were ultimately banished back into nothingness.(K9TV: The Fall of the House of Gryffen)

Mistakenly identified as Ghosts

 * The Cybermen were once mistaken as an army of ghosts. (DW: Army of Ghosts, Doomsday)
 * The Doctor and Sarah Jane Smith were once mistaken for ghosts. (MA: The Ghosts of N-Space)
 * The Gelth were mistaken for ghosts, as their gaseous forms could fly and were a translucent blue. (DW: The Unquiet Dead)