Categories group products or sub-categories together in your catalog and provide control over properties such as price.
You can set pricing rules for one category without setting them for other categories. Each category is an individual instance of a category definition. For example, a category based on the Department category definition (which has the properties Description and Manager) may be named Hardware, and have the properties Power Tools (Description) and Jay Hamlin (Manager).
Each category and product can have one default category. The default category provides a canonical path to a child category or product. If a product is in more than one category, and pricing is set at the category level, only the pricing from the default category is applied to the child categories and products. You can set pricing at the category level by using either category-level pricing or a custom catalog price rule on the category.
You can create product-to-product relationships, product-to-category relationships, category-to-category relationships, and category-to-product relationships. These relationships can be to products and categories in the same catalog, or in different catalogs. For example, in a product-to-product relationship, if you have a customer who buys a movie, you may want to offer the customer the soundtrack to the movie. This is an explicit relationship. In a category-to-category relationship, you can have a relationship between categories. For example, if you have CDs by classical composers, you may also have biographies of classical composers. You may have categories for CDs (by classical composers) and Biographies (of classical composers).
You can specify parent and child category associations. You can create a category that has parent categories or child categories, or both. For example, the category CDs can have the child categories Rock, Rhythm and Blues, and Classical. The child categories can also contain child categories of their own. For example, the category Rock can contain the child categories Pop and Alternative.