This in simple terms means that the insurer will pay your premiums if you cannot work due to injury or illness and this will give you one less worry at a challenging time of your life.
However, there are conditions which will be listed in your policy document and if you meet these conditions you will be eligible to use this option should you need it.
Depending on how long the Waiver of Premium period is, you must pay your premiums for that time and after that time your monthly premiums will be waived.
Many insurers will continue to waive premiums until you are fit to return to work, your policy ends in this time or if you do not fulfil the insurers definition of incapacity. With most policies you need to add this option at the start of your policy.