A sidebar is a user interface element that appears alongside the main content of a webpage or application. It typically contains additional information, navigation links, or tools that enhance the user experience without cluttering the main area. Sidebars can be found in various formats, such as on blogs, news sites, and social media platforms. In web design, sidebars can be static or dynamic, meaning they may remain in place as users scroll or change based on user interactions. They often include elements like search bars, advertisements, or related articles to provide quick access to relevant content and improve site usability.