A red herring, as a metaphor, is anything used as a distraction to draw attention away from the central issue. It can be intentional or accidental.
A herring that has been dried, salted and smoked turns a reddish colour and these cured fish have a particularly strong smell.
One theory for the origin of the phrase is that in medieval times the fish were used as a lure for training hounds in the art of stag hunting.
Later, people who were opposed to fox hunting would drag a red herring across the fox’s trail and entice the hounds away from the scent of their quarry.
Another theory is that escaped prisoners used the smelly herring to put chasing hounds off their trail.
Whichever origin holds the truth a red herring is something to put you off the scent. Or are all our theories just red herrings?