Appellate courts have the authority to correct errors made by trial courts. Specifically, if the appellate court is convinced that the lower court made a mistake that probably affected the case outcome, it may reverse the case.
When appellate courts issue a reversal, they usually send the case back to the trial court with new instructions, which might be to hold a new trial, re-sentence the defendant, or dismiss the case. However, if the appellate court does not feel that the trial court made significant mistakes, it could affirm the judgment, therefore enforcing the outcome or sentence initially imposed.