A cure was a substance, drug, medication, medical treatment, surgical operation, change in lifestyle or philosophy, or any other procedure that solved or healed a patient's medical condition or symptom such as a disease, mental illness, genetic disorder, or a condition deemed undesirable that may or may not result in death. An incurable disease, which may or may not be a terminal illness, did not have a known cure.
In 2364, the answer to Polywater intoxication, including a formula and cure, was downloaded and fed into Doctor Beverly Crusher's medical banks. (TNG: "The Naked Now")