The words these error messages assume you already know.

The list of your products and their attributes that a shopping platform reads. On Shopify it is generated from your product records rather than written by hand.

Machine-readable information embedded in a page so a crawler can understand it without reading the design. For products this is usually JSON-LD following the schema.org vocabulary.

The page a shopper reaches when they click your listing. Google checks that this page agrees with the data you supplied.

Global Trade Item Number — the manufacturer's identifier behind a barcode. Valid lengths are 8, 12, 13 and 14 digits, and the last digit is a check digit calculated from the others.

A specific purchasable version of a product: a size, a colour, a pack. Price and stock belong to the variant, which is why a product-level answer can be misleading.

Whether the item can be bought. Google accepts in_stock, out_of_stock, preorder and backorder.

Our term for the gap that opens over time between your product data and what your storefront actually publishes — usually caused by a theme change, an app or a campaign, and usually silent.