What is Appellant?

Legal Definition
The party who appeals a lower court's decision in a higher court. The appellant seeks reversal or modification of the decision. By contrast, the appellee is the party against whom the appeal is filed.

Suppose P sues D, and wins. D files an appeal. D is the appellant, and P is the appellee. If D wins the appeal, and P appeals, the roles are reversed. P becomes the appellant and D is the appellee.

See Appellate Procedure.
Legal Definition
Practice. He who makes an appeal from one jurisdiction to another.
-- Bouviers Law Dictionary
Legal Definition
The party who takes an appeal from one court or jurisdiction to another.
-- Black's Law Dictionary
Legal Definition
One who files an appeal; the complaining party in an appeal of felony.
-- Ballentine's Law Dictionary