A more thorough explanation:

Joint interest refers to a shared interest or ownership in something. It can be a legal or equitable claim to a property or right.

For example, if two people own a house together, they have a joint interest in the property. They both have a legal claim to the house and share ownership.

Another example is when multiple parties invest in a business venture. They have a joint interest in the success of the business and share in the profits or losses.

Joint interest can also refer to a shared interest in a legal case. For instance, if two people are both plaintiffs in a lawsuit, they have a joint interest in the outcome of the case.