An instance is just a product as can be seen in the refurbed product catalogue. It is the internal depiction of the "lowest level" of a product and its variant at refurbed. Every instance has an instance_id, a name e.g.: "Apple iPhone 12 Mini | 128 GB | purple", a set of attributes which resemble the technical specification and is assigned to a category. We try to keep the names unique and meaningful, so staying with above example, there will only be one "Apple iPhone 12 Mini | 128 GB | purple" in our database and the name contains all information to identify the variant as it was intended by the original manufacturer (also depending on the category though).