a dried, smoked, herring. The curing process turns the fish red.
a false lead, or misleading piece of information intended to divert attention from the real issue (based, according to Brewer's Dictionary of Phrase and Fable, on dragging the smoked fish across a trail to confuse hunting dogs)
a brief for venture capitalists to tempt them into following up with investment in the business plan
Red Herring, a business magazine founded in the dot-com boom of the 1990s, when venture capitalists and business plans abounded.