Goal
Suppose you want to drop the "uPortal" off the url for your portal, i.e. so it can be accessed at "http://my.schoolname.edu".
Solution
Use a context xml file named ROOT.xml with this context:
<Context path="" docBase="ROOT" debug="0" reloadable="true" crossContext="true"/>
What this does is makes uPortal the "default" webapp for Tomcat, telling it to try to use the contents of the uPortal "Context" for those cases where a request didn't map into another configured context.