From Longman Dictionary of Contemporary Englishred herringˌred ˈherring noun [countable] UNIMPORTANTa fact or idea that is not important but is introduced to take your attention away from the points that are important → distraction
Examples from the Corpus
red herring• According to Mattel, antitrust issues were a red herring.• Meg's determination not to see her; her red herring about the mysterious proposal of marriage. 