Norton Virus Protection Promise is a benefit that accompanies many Norton products, including Norton Security. The main point of this benefit is an access to a Norton expert who can help with diagnosing and removing viruses if you get into any sort of virus related problem during your active Norton subscription.
Even though unlikely, but if it happens that Norton expert is unable to remove a virus from your device, you may be entitled into a refund for your Norton subscription.
More information:
How do I check if I have Norton Virus Protection Promise?
A video describing Norton Virus Protection Promise: