In most cases this is a very expensive addition that can be made to any life insurance policy. What it does, is pay the beneficiary a percentage of the life insurance policy, should the insured be killed in an accident that is covered under the policy.
This coverage will often also extend to circumstances in which the insured loses their vision or use of any limbs in an accident. This coverage is generally extremely limited in what it will pay for, so understanding the coverage limits is very important.