A structured custom field on a Shopify resource.
Metafields let you attach typed data — text, number, date, reference, JSON, file, URL — to products, variants, collections, customers, orders and shop. They power PDP customisations, structured filtering, size charts, ingredient panels and integrations that would otherwise abuse tags. Metafields have a namespace and a key (for example `custom.size_chart`) and a defined type; strongly-typed metafields validate on save and are queryable via the Storefront and Admin APIs. Prefer metafields over tags whenever the value has a shape.
