A browser extension is a small software module that adds specific features or functionalities to a web browser. It modifies the browser interface and capabilities, enhancing user experience by integrating additional tools such as ad blockers, password managers, or productivity trackers. Extensions can improve web browsing efficiency, streamline tasks, and personalize the browsing experience. Users can easily install and remove these extensions based on their needs, making them a flexible solution for extending browser functionality without altering the core browser software.