Tomcat is a servlet container (application server?) for serving up Java servlet and Javaserver pages. It can run as a standalone or be configured to work w various http servers.
http://jakarta.apache.org/tomcat/
Below is some of the best instructions I've found for installing on redhat - although they are version specific and not all of the docs apply to newest version.
http://www.linuxgazette.com/issue95/millson.html