A preloader is a visual element that appears on a website or application while content is loading. It helps to inform users that the system is processing their request, reducing frustration during wait times. Common forms of preloaders include spinning icons, progress bars, or animated graphics. Preloaders enhance user experience by providing feedback and maintaining engagement. They are especially useful in applications that require significant loading time, such as those involving large files or complex data retrieval. By using a preloader, developers can create a smoother transition between different states of an application, improving overall usability.