The term insured as the name suggests, more often applies to the insurance industry, but is not exclusive. It can refer to any individual, group of individuals, or property which an insurance policy has been taken out on. To be insured is to be guaranteed against loss, harm, damage, death, or a predetermined event.
This can be applied little things like postal insurance, or more overt policies like Life Insurance that has to be issued by an insurance company. If you have auto insurance, then you vehicle is “insured.” If you have life insurance, then you family is “insured” against your death and will be compensated if you die. There are many different types of insurance, and an exhaustive list of things can be insured. From the contents of your home, to more crazy policies like celebrities getting certain body parts insured.
Some things have to be insured by law, such as your vehicle or even social security, and others are up to the individual or an employer. Some businesses cannot operate without taking out insurance against the wellbeing of their employees. This usually relates to dangerous jobs, but is common in every type of workplace, from offices to Hollywood stunt work.