EJB, or Enterprise JavaBeans, is a server-side software component that encapsulates business logic in Java applications. It simplifies the development of large-scale, distributed applications by providing a framework for building reusable and scalable components. EJBs manage transactions, security, and concurrency, allowing developers to focus on business functionality rather than infrastructure concerns. There are three main types of EJBs: Session Beans, which handle business logic; Message-Driven Beans, which process messages asynchronously; and Entity Beans, which represent persistent data. By using EJB, developers can create robust applications that can easily integrate with other Java EE technologies, enhancing overall productivity and maintainability.