Abuse of discretion is a standard by which appellate courts review certain decisions by lower courts. The standard is used when the appellate court is reviewing a “discretionary” ruling of the lower court judge. For example, administrative agencies are typically given wide discretion in many types of determinations. This, when reviewed by courts, they may be given the benefit of this standard of review.
When the standard is applied, the lower court’s decision will be reversed only if the trial judge made a plain error, exercised discretion not justified by the evidence or made a judgment that is clearly against the facts. Abuse of discretion may also be found when the lower court rests its decision on a clearly erroneous finding of fact, rules in an irrational manner or makes a clear error of law.
Note that this contrasts most sharply with the “de novo” standard, in which appellate courts give no deference to trial court decisions. This is typically applied to judicial findings on questions of law.