When you create your app, you can use metafields to attach specialized information to Shopify resources, such as part numbers or release dates.

Merchants and other apps can retrieve and edit the data that's stored in metafields from the Shopify admin. If you want to use metafields to store data, but you don't want merchants or other apps to access that data, then you can use private metafields.

Metafield definitions enable you to create additional data constraints for metafields, and enable the merchant to edit metafield values in context. Where possible, you should adopt standard metafields, so that your app can access information that merchants have already stored in standard metafields. You can also create your own custom metafield definitions.