red herring

Short definition from Wiktionary

Noun

1. 1
   A herring that is cured in smoke and brine strong enough to turn the flesh red; a typeof kipper.
2. 2
   A clue, information, argument, etc. that is or is intended to be misleading, diverting attention from the real answer or issue.
3. 3
   A red herring prospectus.
4. 4
   A soldier.