Interest relating to the action refers to a legal concept that involves a party's stake or concern in the outcome of a lawsuit, which is essential when determining whether that party has the right to intervene in a legal proceeding. This interest must be direct and substantial, ensuring that the intervenor will be affected by the judgment and that their interests are not adequately represented by existing parties. The notion ensures that individuals with a legitimate concern about a case can join the litigation to protect their rights.