Guaranteed premiums are also known as guaranteed issue life insurance. This is a type of insurance scheme where you can pay a fixed amount of premium no matter what. With guaranteed premiums you know exactly how much money has to be paid as premium from the minute you sign up for the scheme.
The premium amount is hardly ever changed except in rare cases (for example, if you change the principle amount of the insurance). This means that even if there is a fluctuation in the market or different investment performances, you will not need to worry about your insurance policy.
Some people find this kind of policy gives them peace of mind as they know precisely how much their monthly payments are.