Decapitation was the act of removing an individual's head.
Blon Fel-Fotch Passameer-Day Slitheen killed Mr. Cleaver by decapitating him. While disguised as a human, she claimed that he slipped on "a very icy patch". (TV: Boom Town)
Time Lords could still regenerate after being decapitated. Cavisadoratrelundar was decapitated and only killed after being stabbed in both her hearts. (PROSE: The Shadows of Avalon)
A suicide bomber that was still living (due to Miracle Day) even after blowing himself up was still conscious even after his head was detached. (TV: The New World)
Members of the Order of the Headless were decapitated in their initiation. Their heads remained mobile, even after rotting into skulls. (TV: A Good Man Goes to War, TV: The Wedding of River Song)