Products on Back Market are classified into different categories depending on their attributes and characteristics. There are 3 levels of categories, starting with a Category Leaf, then Category Branch, and finally a Category Tree. Category leaves are the most narrow and category trees the most encompassing.
The leaf category defines certain attributes (mandatory and optional) to provide during the creation of a product. Therefore, when creating a product, some fields will depend on the leaf category you selected. Others will always be the same for every product you create.