Overview
Insurable interest exists when an insured person derives a financial or other kind of benefit from the continuous existence, without repairment or damage, of the insured object (or in the case of a person, their continued survival). A person has an insurable interest in something when loss of or damage to that thing would cause the person to suffer a financial or other kind of loss.
Normally, insurable interest is established by ownership, possession, or direct relationship. For example, people have insurable interests in their own homes and vehicles, but not in their neighbors' homes and vehicles, and almost certainly not those of strangers.
The "factual expectancy test" and "legal interest test" are the two major concepts of insurable interest.
Historical background
The concept of insurable interest as a prerequisite for the purchase of insurance distanced the insurance business from gambling, thereby enhancing the industry's reputation and leading to greater acceptance of the insurance industry. The United Kingdom was a leader in that trend by passing legislation that prohibited insurance contracts if no insurable interest could be proven. Notably the Marine Insurance Act 1745 (which introduced the concept of an insurable interest, although it did not use the term expressly), the Life Assurance Act 1774 which renders such life insurance contracts illegal, and the Marine Insurance Act 1906, s.4 which renders such contracts void.
From Wikipedia (CC BY-SA 4.0).