Schema markup is structured data that uses the shared Schema.org vocabulary to describe what content on a page means, for example marking up an article, organization, product, FAQ, or review. It is the specific implementation most people mean when they talk about adding structured data to a site.
For brands, the honest framing is that schema markup is supporting hygiene, not a primary AI-visibility lever. It helps search engines build rich results and parse your pages, but a controlled Ahrefs analysis found near-zero causal effect on AI citations, and most AI assistants do not read schema directly. Implement the standard types cleanly, then put your real effort into content and authority.