A retail customer's purchase request placed through a Participating Organization is known as an order. This is a common term used in the world of finance, specifically in the stock market. When a retail customer places an order, they are essentially requesting to buy or sell a certain amount of a specific stock. This process involves a Participating Organization acting as a middleman to execute the order on the stock exchange. So, when you hear the term "order" in the context of finance, remember that it refers to a customer's request to buy or sell stocks through a Participating Organization.