A more thorough explanation:

A neutrality law is a law that prohibits a country from helping any of the belligerent powers with which the country is at peace. This means that if two or more countries are at war, a neutral country cannot provide military aid to any of them.

For example, the United States has a neutrality law that forbids the country from providing military aid to any belligerent power that is at peace with the United States. This means that if two countries are at war and the United States is at peace with both of them, the United States cannot provide military aid to either of them.

Another example of a neutrality law is the Hague Convention of 1907, which prohibits neutral countries from allowing their territory to be used for military purposes by belligerent powers. This means that if a neutral country allows a belligerent power to use its territory for military purposes, it is violating the neutrality law.

These examples illustrate the definition of a neutrality law by showing how a neutral country must remain impartial in a conflict between two or more belligerent powers. The purpose of a neutrality law is to prevent a neutral country from becoming involved in a war and to promote peace and stability in the international community.