In Elastic Path Commerce, a product is anything advertised for sale in a store. This includes physical items, digital items, services, and gift certificates. Each product has one or more Stock Keeping Units SKU that define the attributes of the product. For example, when a physical item has variations like color or size, each variation has its own SKU. When your customers add an item to their cart, they are adding a product SKU and the quantity of that SKU. And for inventory, the on-hand amount represents the number of each SKU in your inventory.