Argumentum ad nauseam (sometimes argumentum ad infinitum) translates roughly as "argument from nausea": that is, a method of proof in which one attempts to batter down opposition by nauseating repetition of a point.
It is axiomatically fallacious, since repetition of an idea has no bearing on the truth or falsehood of that idea. Unfortunately, it has great utility in the field of demagoguery due to the eager willingness of the hoi polloi to believe The Big Lie.