What is "grandfather paradox"

n. 1 (context uncountable English) The paradox of time travel that hypothetically occurs when one person goes back to the past and kills their biological grandfather before the latter fathered the traveller's father, thus, by extension, preventing the traveller to ever be conceived in the first place. 2 (context countable English) An instance of the grandfather paradox.

The grandfather paradox is a paradox of time travel in which inconsistencies emerge through changing the past. The name comes from the paradox's common description as a person who travels to the past and kills their own grandfather, preventing the existence of their father or mother and therefore their own existence. Any inconsistency in past events may be regarded as a grandfather paradox.

Grandfather Paradox, usually referred to as the Grandfather, is a fictional character in the British science fiction franchise Doctor Who and its spin-off franchise Faction Paradox. In the BBC's Eighth Doctor Adventures novels, the Grandfather is a corrupt future version of the Eighth Doctor, while in Lawrence Miles's Faction Paradox series he is a seemingly incorporeal Time Lord of unknown identity. Both narratives portray him as the founder of Faction Paradox, a time-travelling voodoo cult.