with Entity bean using JPA An entity defines a table (consisting of rows and columns) in a relational database. An entity refers to a logical collection of data that can be stored or retrieved from that entity. For example, in a banking application, Customer and BankAccount can be treated as entities.
Customer name, customer address etc can be logically grouped together for representing a Customer entity. Similarly account number, total balance etc may be logically grouped under BankAccount entity.
with EJB3/JPA Annotations The EJB 3.0 entity beans are used to model and access relational database tables. It is a completely POJO-based persistence framework with annotations that specify how the object should be stored in the database. The EJB 3.0 container does the mapping from the objects to relational database tables automatically and transparently. Their mappings are defined through JDK 5.0 annotations (an XML descriptor syntax for overriding is defined in the EJB3 specification).