A plugin system is a software architecture that allows additional features or functionalities to be added to an existing application without altering its core structure. This is achieved by using plugins, which are separate modules that can be developed independently and integrated into the main application. Examples of applications that use plugin systems include web browsers like Google Chrome and content management systems like WordPress. Plugins can enhance the user experience by providing customizable options, such as new tools or themes. They can also improve performance by allowing users to load only the features they need. This modular approach promotes flexibility and scalability, making it easier for developers to maintain and update software over time.