Which of the following describes an accidental death rider?

An accidental death rider is indeed described as a modification to an existing life insurance policy that provides additional benefits specifically in the event of the insured's accidental death. This rider enhances the base coverage by paying an extra benefit, which is typically a specified amount or a multiple of the death benefit, if the insured dies as a result of an accident.

Accidental death riders are often included in life insurance policies to provide added security and peace of mind to policyholders, recognizing that sudden and unexpected accidents can have significant financial implications for beneficiaries. The benefits provided by the rider act as a buffer against the potential financial hardships that may arise from losing an income earner unexpectedly.

The other choices do not accurately capture the function or nature of an accidental death rider: a standalone insurance policy would not combine coverage with an existing life policy, a guideline for underwriting decisions pertains to how insurance risks are assessed rather than providing benefits, and a legal document of policy terms refers to the main insurance contract rather than a rider that modifies it.