I have to disagree with seotips here, the web is not the whole Internet.  The Web, or the World Wide Web is part of the whole Internet.  It allows ecommerce to operate, which it can't on the Internet given it's technology.  This article will explain the difference:

http://www.webopedia.com/DidYouKnow/Internet/2002/Web_vs_Internet.asp

I've always understood a portal to be an entrance to a collection of works that fall under the same topic -or- a collection of people. 

For a long time AOL and Excite! considered themselves a portal to the Web because of it's larger user base.  That concept is pretty much passe'  and you don't hear the large search properties refer to themselves as portals anymore.

However, topical sites still do.  For example:  http://www.mednets.com/  is a topical portal into the world of medicine.