definition:
A domain is a particular field of thought, activity, or interest, especially one over which someone has control, influence, or rights.
specific words:
Put simply, domain-specific words, also known as Tier 3 words, are technical or jargon words important to a particular subject. For instance, chemistry and element both fall under science-related vocabulary, while allusion and verse relate closely to English language arts (naturally, our favorite subject area).
Examples of areas or 'domains' of knowledge include: Chemistry, Mathematics, Literature, Medicine and History.