What is DefinedTerm schema

Full definition

DefinedTerm is a schema.org type that represents a term with a precise definition within a knowledge system or controlled vocabulary. Its primary properties are name (the term itself), description (the complete definition), termCode (a unique identifier for the term within its set, such as a reference code or slug) and inDefinedTermSet (a reference — either a URL or an embedded DefinedTermSet object — pointing to the vocabulary the term belongs to).

DefinedTermSet is the container type that groups multiple DefinedTerm instances under a shared vocabulary. Its properties are name (the name of the glossary or vocabulary), description (a summary of the vocabulary's scope and purpose) and hasDefinedTerm (an array of DefinedTerm objects).

These types are particularly well-suited to specialist sites that publish technical glossaries, sector dictionaries, regulatory vocabularies or structured reference pages where precision of meaning matters. The markup communicates to any processing system — search engine crawler, AI retrieval pipeline or knowledge-graph builder — that this page is a definitional authority, not an article that happens to mention terms in passing.

Property	Required	Description
name	Yes	The term being defined
description	Yes	The complete definition
termCode	No	Internal identifier within the vocabulary
inDefinedTermSet	Recommended	URL or object reference to the parent vocabulary

Why it matters in 2026

Language models powering AI search engines need authoritative sources when answering definitional questions. A glossary page marked up with DefinedTerm and DefinedTermSet makes an unambiguous structural declaration: this page is a primary source of definitions, not secondary commentary. Without this markup, a model must infer from prose whether the page is the canonical definition or a passing mention.

For a specialist site in the home-improvement, trades or construction sector, a correctly marked technical glossary can become the cited source whenever a user asks an AI assistant what a term means. Capturing that definitional authority compounds over time: each term the site owns as a definition source increases the overall semantic authority of the domain in its sector.

How to implement

1. Create a glossary page with the terms and their complete definitions visible in the HTML. Partial or truncated definitions reduce eligibility for citation.
2. Create the root DefinedTermSet object with name (the glossary title) and description (scope of the vocabulary).
3. Set the url property of the DefinedTermSet to the canonical URL of the glossary page.
4. Add a hasDefinedTerm array containing one DefinedTerm object for each term in the glossary.
5. For each DefinedTerm, set name (the term) and description (the full definition). Both are required for the markup to be meaningful to a consuming system.
6. Add termCode if your vocabulary uses internal reference identifiers — this is recommended for formal or regulated vocabularies.
7. Reference the parent set from each term using inDefinedTermSet pointing to the canonical glossary URL.
8. Validate the complete block using Google's Rich Results Test. Note that DefinedTerm does not currently produce a dedicated Google rich result, but the markup is consumed by knowledge-graph systems and AI retrieval pipelines.

Example

{
  "@context": "https://schema.org",
  "@type": "DefinedTermSet",
  "name": "Heating and plumbing glossary",
  "description": "Technical reference vocabulary for the heating and plumbing trades in the United Kingdom.",
  "url": "https://example.co.uk/glossary/heating-plumbing",
  "hasDefinedTerm": [
    {
      "@type": "DefinedTerm",
      "name": "Combi boiler",
      "description": "A combination boiler is a single unit that provides both central heating and hot water on demand without the need for a separate hot-water cylinder or cold-water storage tank. It heats water directly from the mains supply when a tap is opened.",
      "termCode": "HEAT-001",
      "inDefinedTermSet": "https://example.co.uk/glossary/heating-plumbing"
    },
    {
      "@type": "DefinedTerm",
      "name": "Gas Safe Register",
      "description": "The Gas Safe Register is the official UK list of gas engineers who are legally allowed to work on gas appliances. It replaced CORGI registration in 2009. All engineers working on gas installations in the UK, Isle of Man and Guernsey must be registered.",
      "termCode": "REG-001",
      "inDefinedTermSet": "https://example.co.uk/glossary/heating-plumbing"
    }
  ]
}

Related terms

Schema markup, FAQPage schema, HowTo schema.