Which term refers to definitions relevant to CNG activities?

The term that best refers to definitions relevant to CNG activities is terminology. This term encompasses the complete set of technical words and phrases used in a specific field, like compressed natural gas, capturing not just definitions but also the context in which those terms are used. Terminology includes words specific to the industry's practices, protocols, and technologies, which are crucial for effective communication and understanding among professionals in that field.

While the other choices might seem related, they don’t fully capture the scope of what terminology implies. A glossary typically contains a list of terms with definitions, focusing solely on the definitions without the broader context. Explanations refer to the act of making something clear or understandable, which can pertain to any subject rather than being specific to CNG. Definitions are the meanings of individual terms, yet they do not convey the organized framework and relationships among all terms in the industry that terminology does.