Which prefix indicates "between"?

The prefix that indicates "between" is "inter-". This prefix is commonly used in various medical and scientific terms. For example, "intercellular" refers to the space or activities that occur between cells.

In contrast, "intra-" means "within" or "inside," which denotes something that occurs inside a particular structure or area rather than between them. "Sub-" refers to "under" or "below," which indicates a position or level lower than something else. Lastly, "trans-" means "across" or "through," which suggests movement from one side to another rather than being between two entities. Thus, "inter-" is the precise prefix used to express the concept of being "between."