What does the root "end/o" signify in medical terms?

The root "end/o" signifies "in" or "within" in medical terminology. This prefix is derived from Greek, where "endo" is used to refer to something that is inside or internal to a structure. For example, in words like "endoscope," which is an instrument used to examine the interior of a hollow organ or cavity, the "end/o" indicates that the examination is taking place within that organ. Understanding this root helps in grasping various medical terms that describe locations, conditions, or procedures related to being inwardly situated.

In contrast, the other options demonstrate distinct meanings that do not align with the definition of "end/o." The choice that aligns with outer, middle, or away from lacks the requisite context of internal positioning that "end/o" conveys.