A more thorough explanation:

Definition: According to the nature of the feudal right.

Definition: By or according to natural law.

Example: Ex naturali jure some time may be needed after a declaration of war before the war begins.

Definition: A philosophical system of legal and moral principles purportedly deriving from a universalized conception of human nature or divine justice rather than from legislative or judicial action.

Examples: Gravitation is a natural law. Many ethical teachings are based on natural law.

Explanation: The first example refers to a physical law of nature, while the second example refers to a moral law embodied in principles of right and wrong. Natural law seeks to organize the ideal element in law, furnish a critique of old received ideals, and give a basis for formulating new ones. It yields a reasoned canon of values and a technique of applying it. Natural law demands the abolition of inequality or privilege where it exists.