The argument from ignorance or appeal to ignorance fallacy takes the form “We don’t know this to be false, therefore it is true.” It’s not that a person is ignorant or uneducated about some subject, but rather that they use the lack of discrediting information in order to support a belief or claim that has no rational basis. “I don’t know what those lights in the sky are, therefore they are hyperintelligent extraterrestrials. “Um, but you have no evidence of that claim. Merely you can say that there are lights in the sky and you don’t know what they are.” “You haven’t shown me proof that those lights are not aliens, therefore they are aliens.”
This is an easy trap to fall into when you have a preconceived notion about what the causes of an observation are, and when the data are ambiguous the conclusion is “My premise has not been proven false, therefore it is true.”
Some other examples: Cryptozoologists (like Bigfoot and Nessie hunters) can point out and say “There has been no evidence disproving these creatures, therefore they exist.” Creationists point to biological adaptations that have an (at present) incomplete description of their origin (if that) and say effectively “Science cannot explain this, therefore God did it.”
The whole thing is backwards: the burden of proof is on those who make claims about previously undocumented phenomena, not their doubters. Science cannot prove negatives, you can never prove conclusively that some event will never occur since you’d need complete knowledge about the universe to make such a claim. Rather, any natural theory has an associate probability, where the continued accrual of evidence lends greater and greater validity. To make claims about the natural world because nobody has shown them to be ultimately false does not understand (or does not care about) scientific methodologies and in that regard is bereft of intellectual integrity.