A clue, information, argument etc. that is or is intended to be misleading, diverting attention from the real answer or issue.
A herring that is cured in smoke and brine strong enough to turn the flesh red; a type of kipper.
A red herring prospectus.
Anything used metaphorically to conceal or distract.
Smoke used as a disguise, mask or cover, as of troops in battle.