Jetty and Tomcat are web-containers, while Geronimo, Glassfish and JBoss support the whole J2EE stack (more or less). And, tataaa, they use/include Tomcat or Jetty for web-containers. The most important part of a fullblown J2EE server besides the web-container used to be the EJB-container allowing for deployment of EJBs, having them run in a transactional context etc. Today, J2EE is actually called Java EE. Entity EJBs (JPA) can run outside the EJB-container, say in Tomcat, but then outside the transaction handling that an EJB-container would provide.
