A browser extension is a software program that modifies or enhances the functionality of a web browser. These programs, which are often created by third-party developers, allow users to customize their browsing experience by adding new features, tools, or services to their web browser. Common examples of browser extensions include ad blockers, password managers, and social media tools. Developing browser extensions requires specialized skills in programming languages such as JavaScript, HTML, and CSS, as well as knowledge of various APIs and web development frameworks.