EJB is Enterprise Java Beans. In my understanding it's a competing technology with the Microsoft .NET platform and a critical part of the SunOne platform. Go to http://java.sun.com/j2ee for more info. According to Sun's site,
Enterprise JavaBeansTM is the server-side component architecture for the J2EETM platform. EJBTM enables rapid and simplified development of distributed, transactional, secure and portable Java applications.
Cheers,
cgkanchi