A more thorough explanation:

Definition: A nominal party is a plaintiff or defendant who is included in a lawsuit only because of a technical rule of practice, and who has no real interest or control over the subject matter of the litigation.

For example, in Illinois, every wrongful death action must be brought by and in the names of the personal representatives of the deceased. However, the personal representative may not have any actual interest in the outcome of the case. Instead, the personal representative is included in the lawsuit only because of the legal requirement. In this case, the personal representative is a nominal party.

Another example of a nominal party is a person who is included in a lawsuit simply because they are associated with the real parties in interest. For instance, a company may be sued for the actions of its employees, even if the company had no direct involvement in the incident. In this case, the company is a nominal party.

The Supreme Court has stated that, for diversity purposes, a court must disregard nominal or formal parties and rest jurisdiction only upon the citizenship of real parties to the controversy. This means that a court must focus on the parties who have a real interest in the outcome of the case, rather than those who are included only because of legal requirements.

Overall, a nominal party is someone who is included in a lawsuit only because of a legal requirement or technical rule, and who has no real interest or control over the subject matter of the litigation.