A level death benefit means no matter when the insured dies during the life of the policy, the death benefit proceeds paid out will be level, they do not change over time.
However, with a graded death benefit, such as those for a guaranteed issue life insurance policy, the death benefit may be lower the first two years person is insured, but reaches 100% upon the 2 year anniversary (or three) of the life insurance policy.
What this means is that the insured does not have full coverage under a guaranteed issue life insurance plan the first two years he or she is insured.
The reason for this is that in order to offer guaranteed issue life insurance the insurer may have to accept some people with health issues, and in order to minimize the potential payout of claims for high risk people, the death benefits are limited the first two years of coverage.