The prefix "Exo-" means what?

The prefix "Exo-" derives from Greek, meaning "out," "outward," or "outside." It is commonly used in various medical and scientific terms to indicate something that is external or situated outside of a particular structure or area. For example, in the term "exoskeleton," it refers to a protective outer structure found outside the organism's body.

The other prefixes do not align with this meaning: "within" indicates internal placement (from the prefix "endo-"), "around" suggests a surrounding position (from the prefix "peri-"), and "between" refers to an intermediate space or position (from the prefix "inter-"). Therefore, the choice that accurately represents the prefix "Exo-" is the one that signifies being outside or outward.