When you appeal a case, you "assign error" to things that you think the judge did wrong at trial. One of the most common ones for criminal cases is (in)sufficiency of the evidence which basically says that the evidence in the record did not meet the beyond a reasonable doubt standard. The appellate court will then review the evidence and determine if a "reasonable juror" would be able to find the same verdict from the same evidence. It's essentially just the appellate judges determining if there was enough evidence, but at a slightly looser standard.