A more thorough explanation:

Definition: Identity of interests is a legal term used in civil procedure to describe a relationship between two parties who are so closely connected that suing one of them serves as notice to the other. This means that the other party may be joined in the lawsuit.

For example, if a company is being sued for a product defect, and it is discovered that the company and its subsidiary have an identity of interests, then the subsidiary may also be sued in the same lawsuit. This is because the subsidiary and the company are so closely connected that suing one is essentially the same as suing the other.

Another example of identity of interests is in a divorce case. If a husband and wife have joint property, and the husband is sued for a debt related to that property, the wife may also be joined in the lawsuit because she has an identity of interests with her husband in the property.

These examples illustrate how identity of interests works in practice. It allows for parties who are closely connected to be sued together, which can save time and resources in the legal process.