What is a red herring?

Red herring is an idiomatic expression referring to the rhetorical or literary tactic of diverting attention away from an item of significance. For example, in mystery fiction, where the identity of a criminal is being sought, an innocent party may be purposefully cast in a guilty light by the author through the employment of false emphasis, deceptive clues, ‘loaded’ words or other descriptive tricks of the trade. The reader’s suspicions are thus misdirected, allowing the true culprit to go (temporarily at least) undetected. A false protagonist is another example of a red herring.