Category Mapping is specific to Google Product Categories in Google Shopping which is based on the Google Product Taxonomy Tree, however both Bing And Facebook also accept the same values.

The app is pre-loaded with the entire Google Product Taxonomy, and the Category Mapping Tool is a simple and fast way to apply Google Product Categories to all of your products.

Please note that Google Product Category is REQUIRED for only select product types in Google Shopping including: 

Additionally, for products in the above categories, you cannot JUST use the top-level category (ie Apparel & Accessories). You must extend the tree to at least what is shown above.