New Tags in HTML 5 and Changes

Document Sections in HTML

One of the most significant new features of HTML 5 is the ability to mark up sections of an HTML document using the sectioning tags and related tags, which can identify types of content within a section such as headers, footers and sidebars displayed along with a web page.

Embedding audio and video in HTML 5

There are new tags in HTML 5 that can be used to embed video or audio content in web pages.

Other New Tags in HTML 5
Changes to existing HTML tags
DOCTYPE declaration for HTML 5
There is no DTD in HTML 5. This makes the HTML 5 DOCTYPE declaration much simpler and easier to remember.
<html> tag for HTML 5
In HTML 5, the <html> tag is the same as for the 2000-2010 Recommendations from the W3C HTML Working Group, which includes an xmlns attribute with the namespace URI assigned for HTML elements in 1999. The 1997 HTML 4 standard did not include namespaces yet.
col element
The <col> tag for an HTML table column should not be coded without a colgroup element as its parent.
HTML definition lists

The definition list, definition term and definition description elements are now called description list, description term and detail description respectively. To define a list of terms using the <dl> tag, such as for a glossary, each term defined should be identified by putting it inside a dfn element.