Natural laws are the physical laws that govern the natural world and exist without any human intervention, such as the laws of physics, biology, geology, etc. that control the physical and biological world (and universe).
Two of the most obvious examples of these kind of laws are the earth's rotation and gravity.
These laws have been noted, researched and defined over the centuries by scientists and are often explained in mathematical terms, i.e. Einstein' theory of relativity, and Newton's laws of motion.