A plugin is a software component that adds specific features or functionalities to an existing computer program. By using plugins, users can customize and enhance the capabilities of applications without altering the core software. For example, web browsers like Google Chrome and Mozilla Firefox support various plugins to improve user experience, such as ad blockers or password managers. Plugins are commonly used in various software environments, including content management systems like WordPress and graphic design tools like Adobe Photoshop. They allow developers to create modular extensions, making it easier to update or add new features without affecting the main application.