sidebar
noun [ C ]
uk/ˈsaɪdbɑːr/ us INTERNET
a narrow area on the left or right of a website page giving extra information, often other parts of the website that the user can go to:
Click on items in the sidebar to navigate to other pages.
a narrow area to one side of a newspaper or book page with a short article or other piece of writing in it, usually one that is related to the main information on the page:
Accompanying the article are two sidebars, one showing the letter from the Justice Department.