Use of ";" in URL

Diwakar Shetty <[email protected]> Wed, 04 Sep 2002 19:21:08 +0530

Newsgroups	gmane.comp.web.general
Organization	Oracle
Message-ID	<[email protected]>

I could understand the use of "&" in URL for HTTP requests
"&" separates the <name>=<value> pair

However, what is the use of ";" in URLS ?

Thanks
Diwakar