DefinedTerm is a schema.org type for a word or phrase with a defined meaning — glossary entries, industry jargon, controlled vocabulary — that lets a page declare its definitions as machine-readable entities linked into a DefinedTermSet.
The type is documented at schema.org/DefinedTerm. Core properties: name (the term itself), description (the definition), termCode (short code if applicable), inDefinedTermSet (the parent glossary), and url (the canonical page).
Google does not currently document a rich-result treatment for DefinedTerm, so the type is not a rich-result play. Its value is entity clarity: an answer engine that retrieves a glossary page can see immediately that the page defines a specific term, tied to a parent glossary set, on a specific canonical URL.
Publishers building a glossary should combine three things per term page: DefinedTerm JSON-LD, a visible H1 that is the term, and a visible definition matching the schema description. Group all terms under a single DefinedTermSet node hosted at the glossary index URL.
Cross-link glossary entries to the answer pages that use each term — the internal link lattice is how answer engines discover the depth of coverage on a topic.