Final answer:
The nurse discovered a p.r.n. order, which allows a patient to have 650 mg of acetaminophen every 4 hours for pain relief as needed.
Step-by-step explanation:
The type of order the nurse noticed, which allows the client to have 650 mg of acetaminophen every 4 hours for pain, is a p.r.n. order. The acronym p.r.n. stands for "pro re nata", which is Latin for "as needed". This type of order is used in healthcare settings to give the care team flexibility to administer medication based on the patient's condition and symptoms, rather than at set times. Because the nurse's client requested acetaminophen for a headache, the nurse checks the order and can provide the medication as long as it fits within the prescribed dosing schedule specified by the p.r.n. order.