In Java Enterprise Edition (Java EE), an entity bean is a type of enterprise bean that represents persistent data in a relational database. It is a server-side component that can be used to model the data of an application and provide access to that data from client applications.

There are two types of entity beans in Java EE: container-managed entity beans (CMEBs) and bean-managed entity beans (BMEBs). CMEBs are simpler to develop and manage, while BMEBs provide more control over the persistence logic.

CMEBs are typically defined using an object-relational mapping (ORM) framework such as Java Persistence API (JPA). To create a CMEB, you define a Java class that represents the entity and annotate it with the @Entity annotation. You also define a persistence unit in the persistence.xml file that specifies the database connection details and the mapping between the Java class and the database table. The container will use this information to automatically generate the SQL statements needed to manage the persistence of the entity.

BMEBs, on the other hand, require the developer to implement the persistence logic manually using JDBC or a similar API. To create a BMEB, you define a Java class that represents the entity and implement the javax.ejb.EntityBean interface. This interface provides methods for the container to manage the persistence of the entity, including ejbCreate(), ejbRemove(), and ejbStore().

Once you have created an entity bean, you can use it in your application by injecting it into other components such as servlets or other enterprise beans. You can also define relationships between entity beans to model complex data structures.

Overall, entity beans provide a powerful way to manage persistent data in a Java EE application. Whether you need to model simple data structures or complex relationships between entities, entity beans can help you build scalable and maintainable enterprise applications.