An attribute that is often used to describe the "isness" of a product.
A "product type" attribute is often a difficult one to incorporate into a product hierarchy and schema. Often the values are ambiguous or the level of detail varies from category to category. If the concepts captured in the attribute are broad enough and the distribution of SKUs is appropriate it is possible that it would be used to make the data more granular in the hierarchy and remove it from the schema. This threshold can often be difficult to determine which makes the product type attribute difficult to work with.