A modal window is a graphical user interface element that appears on top of the main content of a webpage or application. It typically requires users to interact with it before they can return to the underlying content. Modal windows are often used for alerts, confirmations, or forms, ensuring that users focus on a specific task without distractions. These windows are commonly triggered by user actions, such as clicking a button or link. They can enhance user experience by providing important information or options without navigating away from the current page. Examples of modal windows include pop-up forms, image galleries, and notification alerts.