A more thorough explanation:

Definition: Contra non valentem is a legal doctrine that states that a limitations or prescriptive period does not begin to run against a plaintiff who is unable to act, usually because of the defendant's culpable act, such as concealing material information that would give rise to the plaintiff's claim.

For example, if a doctor fails to inform a patient of a medical error, and the patient is unaware of the error until after the statute of limitations has expired, the doctrine of contra non valentem may apply. The patient may still be able to bring a claim against the doctor because the limitations period did not begin to run until the patient became aware of the error.

This doctrine is often shortened to "contra non valentem."