HTML5 and Web Page Structure
The aside element was introduced to improve the structure of content for those who require heavy editing features:
Represents a piece of content that is only slightly related to the rest of the page.
(Quite vague, but comes directly from w3.org )
Asides would contain the information often presented in sidebars .
The element can be used for quotes , for advertising, for groups of nav elements, and for information that is considered separate from the main content of the page.
*Use of the new tags article, section, header, footer, hgroup, nav and aside is a matter of the taste or the need of the author.
Note: some of these new elements overlap in purpose.
Aside element accepts Global Attributes.
For a complete list of New Elements visit W3.org