Its heard frequently that yahoo is a web portal,not a web site. So what is a portal and what is a website?
A web site is a collection of information about some particular stuff.A portal on the other hand is not information.It is a collection of services…(not web services). Yahoo provides mail servcie , searching service, shopping service, messaging service under one roof i.e http://www.yahoo.com thats why it is a portal.Similarly google, amazon, ebay are portals which provide many services under one domain.Portals have to exchange info between the existing services and thats why it requires a different setup and framework to make the services go hand in hand. Portals are customizable,websites are not i.e your mail box can be customized as per your needs but not your bookmarked page. The site content of a portal can also be customized owing to your authencity as the user of the portal.
Websites are used to display information. Some of them release feeds throught RSS or Atom. RSS or ATOM feeds are the way of spreading information. News, Blogs, Mails use feeds to provide the same information onto your site. You just need to parse the content present in the feeds which are standardized globally as the RSS 2.0, Atom 2.0. Feeds is a convenient way to extract information from your site which actually was provided by someone else instead of provoking the user to go to the site every time he needs some information thus saving time n travel.