Whole life insurance and universal life insurance are both known as permanent life insurance products. For most people that understanding is good enough, but by design there is something that must be done to make the policy permanent, and the design feature that makes these products permanent is the policy reserve.
Guaranteed universal life insurance has always been a somewhat boring topic to me from a daily professional life point of view. It doesn't fit all that well into my usual paradigm of life insurance plan design, and as a result is often skipped over (rightfully so) by me. However, purely from a thought exercise point of view, guaranteed universal life insurance is quite possibly one of the most fascinating products the industry has ever dreamed up.