Data ghost

A data ghost was the name given to a digital impression of a living consciousness that sometimes remained in the Neural relay of 51st century comm. systems after its occupant had died or been killed.

The dead person would thus appear to be able to still be alive, and be able to communicate, though they quickly became 'confused' due to the degradation of the stored data pattern and started to repeat themselves, or make illogical statements, until eventually the pattern failed. The Doctor described the effect as a footprint on the beach with the tide coming in.

The Data Ghost would communicate through the speaker on the suits, much to the horror of the witnesses to their death. Four of River Song's exploration crew experienced the data ghost phenomenon upon their deaths in The Library: Miss Evangelista, Proper Dave, Other Dave and River Song herself.

However a Data Ghost can be uploaded onto a hard drive and thus would result in the person 'cheating death' while living inside a computer, the Doctor did this as to save River Song who recently just died. (DW: Silence in the Library/ Forest of the Dead)