A more thorough explanation:

Definition: Nonparty refers to a person or organization that is not directly involved in a legal case or contract as a party. In other words, they are not the plaintiff or defendant in a lawsuit or a signatory to a contract.

For example, if two people are involved in a lawsuit, a nonparty could be a witness who has information relevant to the case but is not directly involved in it. Similarly, in a contract between two companies, a nonparty could be a third company that is not a signatory to the contract but is affected by its terms.

Even though nonparties are not directly involved in the legal relationship, they may still have some involvement in the proceedings, such as being called as a witness or being affected by the outcome of the case or contract.