Argumentum ad Ignorantiam (Latin)
Refers to a fallacy of logic in argument, specifically one of the Fallacies of Relevance. The debater using ad Ignorantiam uses an argument from ignorance.
Example:
"I've never heard of anyone flying one of these airplanes, so they don't exist!"
Compare ad hominem, argumentum ad baculum, argumentum ad misericordiam, argumentum ad populum, argumentum ad verecundiam.