The prefix inter- means between or among. The prefix intra- means within. For example, an interstate highway is one that goes between or among states, while an intrastate highway is one that exists only within a single state.
Intra- and inter- can be attached to any common noun without a hyphen—although, as the below examples show, many writers aren’t comfortable doing so. Your spell check might catch your unhyphenated inter-/intra- coinages, but spell check would be wrong.