The phrase can refer to a dried smoked herring, which has been turned red by the smoke, or something, especially a clue, that is usually intended to be misleading or distracting.
Prior to refrigeration kipper was known for being strongly pungent. In 1807, William Cobbett wrote how he used red herrings to lay a false trail, while training hunting dogs and this is probably where the idiom originated.
But Cobbett was not the first to use red herring for scenting hounds. The pamphlet “Nashe’s Lenten Stuffe,” published in 1599 by the Elizabethan writer Thomas Nashe, includes this: “Next, to draw on hounds to a scent, to a red herring skin there is nothing comparable.”
In fiction, particularly in murder mysteries and spy stories, a red herring may be intentionally used by the writer to plant a false clue that leads readers or audiences towards a false conclusion. For example, the character of Bishop Aringarosa in Dan Brown’s The Da Vinci Code is presented for most of the novel as if he is at the centre of the church’s conspiracies, but is later revealed to have been innocently duped by the true antagonist of the story. The character’s name is a loose Italian translation of “red herring.”
I much prefer my red herrings to be in fiction rather than on my plate. And I learned yesterday that I like cow’s cream in my coffee. A friend and I went into a small café to get out of the rain and we ordered coffee. Turns out it was a vegan café and we had a choice of “black” or “coconut milk.” Being venturesome types, we tried the coconut milk. No thanks! Not doing that again. Of course, YMMV (your mileage may vary).