When a lower court decision is entered, both parties generally have the right of appeal. In some specific cases, appeals might not be allowed, particularly if the parties had agreed to abide by an arbitration decision beforehand. If an appeal is entered, though, the parties become the appellant and the appellee.
The person or organization that files the appeal in the matter is the appellant. The appellant has the burden of proof in the case, just like a plaintiff has the burden of proof in a civil case. The appellant must make a case showing that the trial court or judge made some type of error in handling the trial or in rendering the decision. Those errors must be legal errors in relation to understanding and implementing the case law or in handling the procedures of the trial. The appellant does not introduce new evidence in an appeal that might have changed the outcome of the trial case.
The appellant -- or, rather, the appellant's lawyer -- presents the case for a legal error in a written format. Usually, oral arguments are not heard in appeals cases, though there are situations where oral arguments are part of the process.
The appellee is the person or organization on the other side of the case. The appellee usually defends against the appeal because he or she wants to uphold the decision that was made. Sometimes, the appellee defends against specifics in the appeal but might want or be okay with other certain changes in the previous decision. Either way, the appellee also presents arguments via written documents.
The appeals process is typically very formal and requires an understanding of legal briefs and federal court protocols. Working with an experienced appeals attorney is one way to bolster your chance at a positive appeals outcome.
Source: The Judicial Learning Center, "The Appeal Process," accessed July 08, 2016