Patent box is a tax regime that is in place in some countries, such as the United Kingdom, Belgium, and the Netherlands. What it does is decrease the corporate income tax rate for products that are the result of commercialization of an IP in the country. It is trying to link the patents with the products.
For example, in the U.K., it would be something like 5% of the revenues associated with that particular product for a certain length of time, say five years. It gives an incentive to the manufacturers to license or develop IPs in the country, and commercialize them in the country, meaning production in that country.