I don't think they both are clear and distinct defintions.
Usually an EJB container is only a part of a full J2EE enterprise application server which handles the EJB parts of an enterprise application. Some people may use "EJB server" synonymously for either an EJB container or and application server.
On the other hand there are real standalone EJB servers like OpenEJB which can be used for example to add EJB functionality to pure web containers like Tomcat or Jetty.
I hope this makes it somewhat clearer. But don't worry too much about it because confusingly there are often different names for the same things