Earlier quoted context omitted.
It's basically Java SE + a standarized stack of technologies, that are usually used in server applications: Servlet, EJB, CDI, JSP, JSF, JTA, JPA... Java EE is not the only way of doing serverside java apps - most of systems i've developed used tomcat + spring-* stack, which is not a Java EE platform. I think reading this project page may help clarify what Java EE is: http://openejb.apache.org/apache-tomee.html
Spring + tomcat is built on J2EE, or at least it was 5 years ago when I worked on that stuff. The servlets API is part of J2EE.
These days it's more fair to say that Spring "supports optional integration" with JEE API's. You can run modern Spring web/REST apps without a Servlet container. Spring doesn't care whether your ORM implements the JPA interfaces or not. Etc, etc... it's all slowly phasing out.