Final answer:
A flat, discolored area on the skin of a 9-month-old baby would be described as a macule in medical records.
Step-by-step explanation:
In the context of a physical examination of a 9-month-old baby with a flat, discolored area on the skin, a nurse would describe this as a macule. A macule is defined as a smooth spot of discoloration on the skin that is not raised above the surface. Therefore, in medical terminology, when documenting in the medical record, the nurse would note the presence of a macule.