What does the prefix "epi-" indicate in medical terminology?

The prefix "epi-" is derived from Greek, meaning "upon" or "above." In medical terminology, it is commonly used to indicate something that is situated on the outer surface or is external to a structure. For example, the term "epidermis" refers to the outer layer of skin. This aligns with the concept of "outer" or "above," highlighting how "epi-" describes a position relative to other anatomical parts. Understanding this prefix helps in interpreting numerous medical terms where it indicates location or surface features.