Red herring

herring which is salted and smoked to a dark brown color; something designed to change a subject, something that diverts attention

A red herring is a metaphor for a diversion or distraction from an original objective. An example can be found in academic examinations, particularly in mathematics and physical sciences. In some questions, information may be provided which is not necessary to solve the given problem. The presence of extraneous data often causes those taking the exam to spend too much time on the question, reducing the time given to other problems and potentially lowering the resulting score. Red herrings are frequently used in literature and cinema mysteries, where a character is presented to make the reader/viewer believe he/she is the obvious perpetrator, when in reality it is someone far less suspect.
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Noun
1. any diversion intended to distract attention from the main issue
(hypernym) diversion, deviation, digression, deflection, deflexion, divagation
2. a dried and smoked herring having a reddish color
(synonym) smoked herring
(hypernym) herring
3. a first draft of a prospectus; must be clearly marked to indicate that parts may be changed in the final prospectus; "because some portions of the cover page are printed in red ink a preliminary prospectus is sometimes called a red herring"
(synonym) preliminary prospectus
(hypernym) course catalog, course catalogue, prospectus

A preliminary prospectus containing information required by the S.E.C.. It excludes the offering price and the coupon of the new issue.