A more thorough explanation:

A national-treatment clause is a provision found in some treaties, particularly commercial ones, that grants foreigners the same rights as those given to nationals in certain aspects.

For instance, if a country has a national-treatment clause in its trade agreement with another country, foreign companies operating in that country will be treated the same way as domestic companies. This means that they will have access to the same benefits and protections as local companies, such as tax breaks, subsidies, and legal rights.

Another example is in the field of intellectual property. If a country has a national-treatment clause in its patent law, foreign inventors will be granted the same patent rights as domestic inventors. This means that they will be able to apply for and receive patents on their inventions, just like local inventors.

These examples illustrate how a national-treatment clause can promote fairness and equality in international trade and intellectual property rights. By granting foreigners the same treatment as nationals, countries can encourage foreign investment and innovation, which can benefit both their own economy and the global economy as a whole.