A portlet is a component that can exists in a component container
in this case container is the Portal .
a portal handle lifecycle of portlets , security and access rules, decoration .....
you can create roles and users in a portal system , and ssign each role permission to have access to some portlets ...
you use a portal to show ,for example, multiple portlets in one page .
each portlet can bring information from diffrent sources and allows visitor /user to see those information or manage them.
for example ,
http://my.yahoo.com is a portal , each of those informational panel is a portlet (those are not jsr or
java based though).
http://www.google.com/ig is another portalwith several portlet on it
hth