Explanation:

- Ratio Decidendi: This is the legal principle or rule that forms the basis of a court's decision. It serves as the authoritative element of a judicial decision, guiding future cases.

- Res Ipsa Loquitur: A Latin phrase meaning “the thing speaks for itself.” It's used in tort law to indicate that the nature of an accident implies negligence.

- Quid Pro Quo: This means "something for something" in Latin. It refers to an exchange of goods or services, where one transfer is contingent upon the other.

- Per Incuriam: This term means "through lack of care." It is used when a judgment is passed without considering the relevant law or facts.

Quid Pro Quo is the correct answer.