What term describes vocabulary used exclusively by a specific group of people?

The correct term for vocabulary used exclusively by a specific group of people is jargon. Jargon refers to specialized terminology that is specific to a particular profession, industry, or group, and it often includes words and phrases that may not be understood by those outside that group.

In contrast, slang refers to informal language that is often used within particular social groups but can vary widely and change over time. Onomatopoeia is a term that describes words that imitate sounds, like "buzz" or "sizzle," and is not related to a specific group’s vocabulary. Metaphor involves a figure of speech in which one thing is described as if it were another, and it also does not pertain to exclusive vocabulary used by a specific group. Therefore, jargon is the precise term that captures the essence of vocabulary unique to a certain collective.