Product structured data (Schema.org)
Product structured data is the part of a product page written for machines: the name, price, availability, identifiers and attributes in Schema.org's vocabulary, usually as a JSON-LD block in the page's head.
What assistants read from it
A Product with its name, description, image, brand, SKU and GTIN, and an Offer with price, currency and availability, is the first thing a crawler reads. Attributes beyond those (material, colour, size, pattern) can be stated as additional properties. An assistant that cites a page has read this block. A page without one is read as prose, and prose is matched less reliably because the crawler has to guess which number is the price.
Where stores get it wrong
The markup disagrees with the page: an old price, an availability nobody updates, a variant's facts stated on the parent. The theme's default markup gives the name and price and stops. Variant pages and collection pages carry none at all. Any of these gives the assistant a reason to trust the page less than a competitor's.
What Sighted does
Sighted generates per-product Schema.org JSON-LD from your approved data, including the attributes it wrote, and a Shopify theme extension puts it on your product pages so that the page and your feeds agree.
See how the assistants read your store.