Which of the following describes the position of a patient who is supine?

The term "supine" specifically refers to a position in which a person is lying on their back, facing upwards. This position is commonly used in various medical examinations, treatments, and while a patient is resting. It facilitates access to the patient's body for various procedures and is a comfortable resting position for many individuals.

The other positions described do not align with the definition of supine. Lying on the stomach refers to the prone position, lying on the side refers to lateral positioning, and sitting upright defines an erect posture, none of which match the criteria for being supine. Thus, understanding the term "supine" as lying on the back is essential for medical professionals to accurately describe patient positioning and ensure proper care.