Each year that you drive without making a claim, you get another year’s NCD (or no claims discount, often called no claims bonus, or NCB). This gives you a bigger discount on your policy price. Protected NCD is an optional add on that helps to protect the discount that you have earnt over the years.
However, it does not protect you from your total policy price from going up at renewal, especially if you have made a claim. It's also important to know that there is a limit to the number of claims this can cover in a certain time.
For more information check out our full article from the Know Your Policy series: Understanding how to protect your no claims discount.