A more thorough explanation:

Term: Ratio Legis
Definition: Ratio Legis is a Latin term that means the reason or purpose behind making a law. It is the underlying motive or intention that drives lawmakers to create a particular statute. For example, the ratio legis behind a law that prohibits smoking in public places is to protect non-smokers from the harmful effects of second-hand smoke. Similarly, the ratio legis behind a law that mandates seatbelt use is to reduce the number of fatalities and injuries in car accidents. In essence, ratio legis is the rationale or justification for a law's existence.