The fragment identifier (also known as: Fragment IDs, Anchor Identifiers, Named Anchors) introduced by a hash mark # is the optional last part of a URL for a document. It is typically used to identify a portion of that document.
<a href="http://www.someuri.com/page#fragment">Link to fragment identifier</a>
Syntax for URIs also allows an optional query part introduced by a question mark ?. In URIs with a query and a fragment the fragment follows the query.
<a href="http://www.someuri.com/page?query=1#fragment">Link to fragment with a query</a>
When a Web browser requests a resource from a Web server, the agent sends the URI to the server, but does not send the fragment. Instead, the agent waits for the server to send the resource, and then the agent (Web browser) processes the resource according to the document type and fragment value.
Named Anchors <a name="fragment"> are deprecated in XHTML 1.0, the ID attribute is the suggested replacement. <div id="fragment"></div>