The level premium period applies to term insurance because whole-life and many universal life policies offer a level premium for your entire lifetime.
Term life insurance has premiums that go up and get more expensive every year. Most people that buy term pay extra for a level premium for a certain period. That way you can keep the premium affordable for 20-years or so and usually you cancel the policy after that period of time because it will be way more expensive if you try to continue it after that.
Level Premium Life Insurance is term life insurance that is guaranteed to stay the same price for the entire term. Some term policies are advertised as level premium, but the policy is only guaranteed to stay level for part of the term. There are term policies that can have a level premium period of 30 years or more.
Term life insurance has premiums that go up and get more expensive every year. Most people that buy term pay extra for a level premium for a certain period. That way you can keep the premium affordable for 20-years or so and usually you cancel the policy after that period of time because it will be way more expensive if you try to continue it after that.