A sidebar is a section next to the main content of a web page, usually placed vertically. Sidebars are used on websites to host additional information, navigation elements, advertisements, links, profile information, search boxes, recent posts or other widgets (small tools). The purpose of the sidebar is to assist users in navigating the website and to offer additional content or functions.

Sidebars can be located on the right, left or both sides depending on the design and needs of the web page. Some websites can dynamically change the sidebar or remove it altogether, depending on the content of the page. Especially in content management systems like WordPress, the content and layout of sidebars can be easily customized and managed, making them a highly flexible and useful tool for websites.