An Enterprise JavaBeans (EJB) container provides a run-time environment for enterprise beans within the application server. The container handles all aspects of an enterprise bean's operation within the application server and acts as an intermediary between the user-written business logic within the bean and the rest of the application server environment.
EJBContainer is for EnterpriseJavaBeans as ServletContainer is for JavaServlets. EjbContainer gives the EJB some lower level services like
Life Cycle Management
With these lower level services the programmer need not worry about some of the issues that he had to take care while doing traditional way of programming (like in Java Servlets). Without the container the EJB's cannot be executed, in one way you can think of the EJB container as the EJB Server.