Ad stacking refers to the practice of displaying multiple advertisements on top of each other within the same webpage or app, often in an attempt to increase the chances of user engagement and click-through rates. This technique is commonly used by advertisers to maximize their reach and visibility, but can also be seen as intrusive and disruptive to the user experience. Ad stacking can also refer to the act of placing multiple ads in a single ad space, which can lead to cluttered and overwhelming visuals.