Double indemnity refers to a specific clause that generally only arises in life insurance policies. A double indemnity life insurance policy is a life insurance policy which effectively would result in double payment in the case that the individual holding the policy suffers an accidental death. An accidental death is specifically defined within a double indemnity clause as being a death which is neither caused by natural causes nor is caused by some human will.
For example, an individual who was consciously murdered by another would not have suffered an accidental death; neither would an individual who died from cancer. But an individual who died as the result of an accident, such as a car swerving and hitting him or her when he or she was walking on the sidewalk, might then qualify for the double indemnity policy to come into effect.
A double indemnity clause might be listed and mentioned in a letter of indemnity, which is a specific form of documentation which might set out any important indemnity clauses between two parties. A letter of indemnity, such as an indemnity form, would essentially set out the provisions under which indemnity would be paid and would act as a promise from one party to pay indemnity under those conditions.
As such, for double indemnity to be paid, it normally would have to be mentioned in the letter of indemnity or in some equivalent indemnity form.