Enterprise JavaBeans (EJB) is a server-side software component that encapsulates business logic in Java applications. It simplifies the development of large-scale, distributed applications by providing built-in services such as transaction management, security, and concurrency control. EJBs are designed to be reusable and can be deployed on any compliant Java EE server. EJBs come in three main types: Session Beans, Entity Beans, and Message-driven Beans. Session Beans handle business processes, Entity Beans represent persistent data, and Message-driven Beans facilitate asynchronous communication. This architecture allows developers to focus on business logic while the EJB container manages the underlying complexities.