“Terminology” means a set of specialized words specific to an area of study. These words are usually not commonly used outside of that area – for example, you probably wouldn’t use the word “igneous” unless you were talking about volcanic rocks or geology in general.

Example: “One of the reasons that legal systems can seem hard to understand is that not everyone knows the terminology used in law, and words like ‘obligor’ and ‘pendency’ are not in common use.”