J2EE Server:
A middleware solution which confirms to the J2EE standards. Sun has a J2EE certification process for servers to test their compatibility with J2EE standards. Not all J2EE servers are Sun certifiied.

J2EE systems typically include Web servers, application servers, messaging software, and increasingly Web-services engines. J2EE is an umbrella specification that includes many popular technologies: Servlets, JSP, EJB, JMS, and the Java Web-services APIs (SAAJ and JAX-RPC) are all part of J2EE.
From : www.objectinnovations.com/Guides/JavaVersions.html