Final answer:
The term 'prn' stands for 'pro re nata', a Latin phrase used in prescriptions that means 'as needed'. It is used to indicate medication should be taken only when necessary.
Step-by-step explanation:
Among the options provided, prn stands for pro re nata, which is a Latin phrase that translates to 'as the situation demands' or 'as needed' in English. This term is often used in medical prescriptions to indicate that a medication should be taken only when necessary, depending on the patient's condition or symptoms, rather than being taken on a regular schedule.