The Taxonomy API enables you to assist both sellers and buyers:

• It helps sellers to determine the best eBay category under which to offer each inventory item for sale in a selected eBay marketplace. It helps sellers to select the categories of items to include in a campaign or promotion. It also provides information about the aspects to include when defining an inventory item in a given category. For more information, see the Selling Integration Guide.
• It helps buyers to determine the appropriate categories in which to browse or search for the items they're looking to purchase in a particular eBay marketplace. For more information, see the Buying Integration Guide.