Terminology is vocabulary associated with a certain field of study, profession, or activity. Knowing the terminology is an important part of being able to work in a given profession.
When your nuclear physicists friends start talking shop and it suddenly sounds like they are speaking a different language, they are probably using nuclear physics terminology. Education terminology includes "rubric," "lesson plan," "pop quiz," "term paper," "student engagement." Medical terminology includes "blood work," "CVC," "scalpel," "set." Lawyers sometimes use legal terminology such "forthwith," "heretofore" and "the part of the first part" to intimidate people they might want to threaten to sue. It works.