schema.org
schema.org is the shared vocabulary that structured data uses to describe things on the web. It defines standard types like Product, Offer, and Review that a search engine or AI agent understands the same way across every site.
How it works
Think of it as the agreed set of words. schema.org gives you the type Product and the properties an agent expects on it (name, brand, gtin, offers, and so on), and JSON-LD is the format you write those words in. It is maintained jointly by Google, Microsoft, and other search companies.
A commerce example
Marking a page as a Product with an Offer that carries price and availability, and a Review with a rating, tells an agent exactly what it is looking at, instead of leaving it to infer from the text.
What this means for your store
Use the Product, Offer, and Review types as fully as your catalog allows. The more of the standard vocabulary you fill in, the more an agent can compare and trust your product.