What does "jargon" refer to?

"Jargon" refers specifically to shorthand phrases or specialized vocabulary that is understood primarily by a particular group of people. This specialized language often arises in specific contexts, such as professions, fields of study, or hobbies, where individuals develop a unique set of terms that may not be familiar to those outside the group. Understanding jargon is crucial for effective communication among professionals or enthusiasts within that specific area.

For example, in medicine, terms like "hypertension" or "myocardial infarction" are commonly used among healthcare professionals, but might confuse a layperson. This distinction is what makes the term "jargon" unique, as it highlights the exclusionary aspect of this type of vocabulary—it is not commonly known and can create barriers to understanding for those not versed in that field. This is why the answer is correct in identifying jargon as a specialized vocabulary rather than common phrases, formal written language, or mainstream terminology.