The <aside> tag has been added to HTML5 to define a section with additional information related to the content around the aside element. It is generally used to enhance an article with additional information, or highlighting parts that can be interesting to the user. Content in aside is a stand-alone, non-essential part of the web page, and if you delete it, the main content will not be affected.
Endnotes comments, reference information, lists of terms, a collection of links, pull-quotes, etc. are a kind of information that can appear in the <aside> element.
Do not confuse the <aside> element with sidebar. Sidebar is just a visual element, and the <aside> tag doesn’t systematically look like a sidebar.
The <aside> tag comes in pairs, which means that the content is written between the opening (<aside>) and the closing (</aside>) tags.
<html> <head> <title>Title of the document</title> </head> <body> <p>I like watching Game of Thrones.</p> <aside> <h4>Game of Thrones</h4> <p>Game of Thrones is an American fantasy drama television series created by David Benioff and D. B. Weiss. It is an adaptation of A Song of Ice and Fire, George R. R. Martin's series of fantasy novels</p> </aside> </body> </html>