Form dictionary.com:
por‧tal
1.a door, gate, or entrance, esp. one of imposing appearance, as to a palace.
2.an iron or steel bent for bracing a framed structure, having curved braces between the vertical members and a horizontal member at the top.
3.an entrance to a tunnel or mine.
A portal can be many things, but in
Java, it has to do with a website that is backed up by the Portal API. That means built in user customizations, single sign on, and edit features, for the most part.
I did a tutorial to answer just the very question you are asking. It's very popular, and demonstrates what a Portal, such as WebSphere Portal, is all about. Enjoy:
http://www.technicalfacilitation.com/multimedia/portal/01%20intro/portalintro.html -Cameron