Genetic genealogy, like documentary genealogy, can result in negative findings and negative evidence. What’s the difference? (It wasn’t that long ago that I was confused about that too!)
You start with a research question and a source. ‘Negative’ means the information you’re looking for in the source isn’t found. A negative finding doesn’t help you answer your research question. Negative evidence does. You may have to understand the context to know which one you have. Some examples, with document-source genealogy and DNA-source genealogy, may help.