A Red herring is anything that turns out to be totally irrelevant to the question at hand. For example, in criminal investigations, detectives (rightly) follow nearly any lead they are given; most turn out to be "red herrings". The hope is that one will not. The same is true of scientific investigations.
Red herrings are sometimes intentionally introduced in a debate (political or otherwise). Skilled debaters are good at detecting this. For example, during an election campaign, a politician who is weak on the economy might make a speech attacking a rival on a much more trivial issue, such as a politically incorrect remark he or she may have made some time ago. The hope is that the electorate and the media will focus attention on the red herring and overlook the campaigner's poor economic record.