A more thorough explanation:

Natural law is a set of moral and legal principles that come from nature or divine justice, rather than from laws made by people. It is based on the idea that there are certain things that are right and wrong, regardless of what any government or society says. For example, many people believe that it is wrong to kill or steal, even if there is no law against it. Natural law is sometimes called "philosophical jurisprudence" because it is a way of thinking about what is fair and just. It can be used to criticize existing laws and to create new ones that are more in line with what people believe is right.