appellant – The party bringing the action to court (usually an appellate/appeal court).
In law, an appellant is the party who, having lost part or all their claim in a lower court decision, is appealing to a higher court to have their case reconsidered. This is usually done on the basis that the lower court judge erred in the application of law, but it is also usually possible to appeal on the basis that the court misconducted itself, or that a finding of fact was an entirely unreasonable one to make on the evidence. The responding party is called the “appellee.”
The appellant in the new case can be either the claimant, defendant, or respondent from the lower case, depending on who was the losing party. The winning party from the lower court, however, is now the respondent. In unusual cases the appellant can be the victor in the court below, but still appeal. For example, in Doyle v Olby (Ironmongers) Ltd [1969] 2 QB 158, the claimant appealed (successfully) claiming that, although he won in the court below, the lower court had applied the wrong measure of damages and he had not been fully recompensed.
By convention in some law reports, the appellant is named first. This can mean that where it is the defendant who appeals, the name of the case in the law reports reverses once (or, in some cases twice) as the appeals work their way up the court hierarchy. This is not always true, however. In the United States federal courts, the parties names always stay in the same order as the lower court when an appeal is taken to the circuit courts of appeals, and are re-ordered only if the appeal reaches the United States Supreme Court.