Entity represents a single object instance that is typically related to one table. Any Plain Old Java Object (POJO) can be converted to an entity by annotating the class with @Entity. Members of the class are mapped to columns of a table in the database. Entity classes are simple Java classes, so they can extend or include other Java classes or even another JPA entity. We will see an example of this in our application. You can also specify validation rules for members of the Entity class; for example, you can mark a member as not null using the @NotNull annotation. These annotations are provided by Java EE Bean Validation APIs. See https://javaee.github.io/tutorial/bean-validation002.html#GIRCZ for a list of validation annotations.