Lazy loading is a technique used in web development to optimize the performance and efficiency of a website or app. Lazy loading involves delaying the loading of certain resources, such as images or videos, until they are needed by the user. This can reduce the amount of data that is transferred over the network, and can improve the overall speed and responsiveness of the website or app. Lazy loading is often used in advertising, as it can improve the performance of ad content, and can make it easier for ads to be delivered to users in a timely and efficient manner. Lazy loading can be implemented in a variety of ways, and can be customized to meet the specific needs and requirements of a website or app.