The name of the ScrumProcess is not an acronym. It (inaccurately?) comes from Rugby.
The authors of Scrum don't spell it SCRUM. It doesn't really matter, but SCRUM implies an acronym, whereas Scrum doesn't.
From scrum or scrummage 1 : a rugby play in which the forwards of each side come together in a tight formation and struggle to gain possession of the ball when it is tossed in among them 2. British : MADHOUSE or a badly organised queue.