Aside

The HTML   element was introduced in HTML5. It defines some content aside from the content it is placed in. This content should be related to the surrounding content. The content could also be placed as a sidebar in an article. Such sections are often represented as sidebars or as inserts; they often contain side explanations like a glossary definition, more loosely related stuff like advertisements, the biography of the author, or in web-applications, profile information or related blog links. This element must not be descendant of an  element.

Attributes
See Global HTML Attributes and Standard HTML5 Attributes.

HTML example:

Ever heard of The Epcot center? Epcot Center The Epcot Center is a theme park in Disney World, Florida.

Rendering
The aside element by itself does not have a visual rendering, other than being a block element. It does however influence the rendering of the element, see that page for more information.

Coding rules
The element belongs to the Flow content category.