Supine: This refers to having the back or dorsal surface downward. A person who is in a supine position is lying face up as opposed to prone.
For a more complete listing of terms used in medicine for spatial orientation, please see the entry to "Anatomic Orientation Terms".
From 
References
Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.