Product type is a sub category in an eCommerce website that includes products of the same nature for easily benchmarking prices, attributes, sales volume and more. In many eCommerce websites it will be 4th level (L4) subcategory.
For example in Amazon: Home & Kitchen (L1) > Furniture (L2) > Bedroom Furniture (L3) > Nightstands (L4)
Customer may request several product types (L4 categories) from one L3 sub-category or from different ones in the same L1 (top) product category