Which term describes the meaning of the prefix exo- in medical terminology?

• A. Inside
• B. Outside
• C. Across
• D. Above

Answer: (B)

Exo- denotes outside or external. In medical terms, this prefix shows that the root refers to something located on the outside of a structure or the body. For example, exocrine glands secrete substances outside into ducts, and exophthalmos describes the eye bulging outward. By carrying the sense of outward relative position, exo- straightforwardly means outside, which is why the correct term in this question is outside. The other directions don’t fit because they describe inward locations or different directional ideas (inside would use endo-, and terms for across or above use other prefixes such as trans- or epi-/super-).