About EJB References

EJB references are intra-bean (bean-to-bean) calls. These are not for use by clients, but for when one bean wants to call methods on another bean.

EJB references can be external and/or internal (local).

External references are when the calling bean is deployed in another EJB module, possibly on another server.
Internal (local) references are used when the calling bean is in the same EJB module as the called bean.