: “To draw a red herring across the track” (cf. quot. 1686 . . . ): to attempt to divert attention from the real question; hence “red-herring,” a subject intended to have this effect.

: [The “quot. 1686”:] “The trailing or dragging of a dead Cat, or Fox, (and in case of necessity a Red-Herring) three or four miles . . . and then laying the Dogs on the scent” (Nicholas Cox, “The Gentleman’s Recreation,” 1686).

: (Red herrings are literally herrings that turn red when cured by smoking.)

A red herring is an alternative, somewhat old fashioned, name for a smoked herring. Such fish have a very strong smell and were usually known, not as kippers, but as red herrings in many parts of 19th century Britain. Because of their smell they were good at masking other smells; as a result they could easily cover the scent of a fox. A red herring pulled across the trail could divert the hounds onto a false path. Thus, by analogy, the phrase came to be used to describe any false trail

Smoking a herring turns it red.

According to the Oxford English Dictionary, the term was first used in print in 1863.

A “red herring” argument is one which distracts the audience from the issue in question through the introduction of information that is unnecessary or irrelevant.

RE:
What does the term "a red herring" mean? Where did it come from?

“A Red Herring” comes from the 1947 suspence film “The Spiral Staircase” where one person ‘Mr. Oates’ is appeared to be the murderer when he is not though he looks sinister. Making him, the “Red Herring”.

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