1
general::
Something that draws attention away from the central issue, as in Talking about the new plant is a red herring to keep us from learning about downsizing plans. The herring in this expression is red and strongsmelling from being preserved by smoking. The idiom alludes to dragging a smoked herring across a trail to cover up the scent and throw off tracking dogs. [Late 1800s]
American Heritage Idioms
2
general::
Phrase(s): a red herring
a piece of information or suggestion introduced to draw attention away from the real facts of a situation. (A red herring is a type of strong-smelling smoked fish that was once drawn across the trail of a scent to mislead hunting dogs and put them off the scent.) • The detectives were following a red herring, but they’re on the right track now. • The mystery novel has a couple of red herrings that keep readers off guard.
McGrawhill's American Idioms And Phrasal Verbs