Life insurance is a fairly straight forward idea but there are several variations around the main two types.
Level term insurance gives you the same amount of cover right up to the end of the term of the insurance. Decreasing term insurance pays out a decreasing amount over the years of the term.
Although it seems strange that an insurance policy would be designed to pay out less and less as the years go by the usual reason for someone taking out such a policy is to directly cover a repayment mortgage where the amount owed also decreases over the years. The policy will be carefully calculated to make sure that any time during the term the lump sum paid out will cover the total outstanding on the mortgage.