Perishable inventory consists of products that expire or lose value over time, eventually becoming worthless. Sometimes product quality perishes gradually, like a market research report that becomes less relevant (and, therefore, less valuable) as time goes on, and sometimes it happens instantaneously, like the value of a ticket for a seat on an airplane after the plane takes off. Perishable inventory and perishable stock are often used interchangeably, but, in practice, sometimes they are equivalent and sometimes they aren't. Perishable stock tends to specifically refer more to perishable goods that can be stocked. Yogurt and floral bouquets are both perishable inventory and stock, while rounds of golf and nights in a hotel are perishable inventory but can't be stocked in a refrigerated warehouse like yogurt. While some of the techniques and strategies discussed here apply to all kinds of perishable inventory, the focus is on perishable stock. Revenue management strategies focus on maximizing profits from non-stock perishable inventory, such as hotel nights, airline tickets and rounds of golf.