Enterprise JavaBeans (EJB) is a technology for building scalable, robust, and secure distributed applications in Java. It provides a framework for creating and deploying server-side components or "beans" that can be accessed by other Java applications, web services, and clients.

EJB provides many features such as security, transaction management, concurrency control, and persistence that are essential for enterprise applications. With EJB, you can create complex applications that can handle high loads and provide high availability and reliability.

There are two types of EJBs: session beans and entity beans. Session beans represent business logic and are used for processing requests from clients. Entity beans represent persistent data and are used for accessing and storing data in a database.

EJB is part of the Java EE (Enterprise Edition) platform, which includes other technologies such as Servlets, JSP, and JMS. Java EE provides a complete platform for building enterprise applications that can be deployed on various application servers such as JBoss, Weblogic, and Websphere.

Learning EJB requires a good understanding of Java programming, object-oriented design principles, and enterprise application architecture. It is also important to have knowledge of related technologies such as JDBC, JNDI, and JTA.

In summary, EJB is a powerful technology for building enterprise applications in Java. It provides a framework for creating scalable, reliable, and secure server-side components that can be accessed by various clients and services.