Coverage length for a life insurance policy means the length of time that your life insurance policy will stay In effect - how long you will have the life insurance coverage. 

Usually, the coverage length of a life insurance policy is referring to how long the policy will stay in effect at a level premium (level meaning the premium is guaranteed not to go up).

The life insurance coverage length assumes that premium payments are made on time and if a policy loan is taken from the cash value inside the policy (permanent life insurance), that it is repaid per the policy guidelines.

Usually, a term life insurance policy has level premiums for a period of up to 30 years, while a permanent life insurance policy has guaranteed level premiums for your entire lifetime.

So, term life insurance offers temporary coverage while permanent life insurance provides lifetime coverage.