A more thorough explanation:

An outside party is someone who is not directly involved in a legal case or agreement, but is still affected by it in some way.

• In a divorce case, the children of the couple are considered outside parties.
• In a business contract, a supplier who is not a signatory but whose goods or services are essential to the contract is an outside party.

These examples illustrate how an outside party is someone who is not directly involved in a legal case or agreement, but their interests or rights may be affected by the outcome of the case or agreement.