We hear the term ‘red herring’ used often, especially in mystery stories.

Where does it mean and where did it come from?

A red herring is something that misleads or distracts from finding the truth. Writers use the device to lead readers and audiences toward a false conclusion. 

Red herrings must be credible to be effective.

The term became popular when William Cobbett told a story on how dog trainers used strong-smelling fish to mislead dogs into following false trails.