Faction (noun), in political terminology, is usually a small organized dissenting group within a larger one.
Faction, relating to books and films, is a common well-used term implying that whilst fiction they are loosely based upon fact. Books in the faction genre are made up of stories based on historical figures or events that are woven together with fictitious elements. This genre, more than any of the fiction historical genres, pushes the limits of what is a real historical event or personal and what is not. The line between the truth and what is fiction is extremely blurred in this genre; it tends to confuse people as to what is true historical information and what is not.