Which term is used to describe the position of a body lying down on its side?

The term that describes the position of a body lying down on its side is "lateral." This position accounts for either the left or right side of the body being down, which is significant in various medical contexts, such as examinations, procedures, and patient comfort. Understanding this position is important in clinical practice, particularly for assessing patients, administering treatments, or ensuring proper positioning to avoid pressure sores.

In contrast, "supine" refers to a person lying on their back, and "prone" describes a person lying face down. "Sitting" indicates an upright position, which is not lying down at all. Therefore, lateral is the most accurate term for describing a body positioned on its side.