What are JPA entities?

An Entity is roughly the same thing as an instance of a class when you are thinking from a code perspective or a row in a table (basically) when you are thinking from a database perspective.

So, it's essentially a persisted / persistable instance of a class. Changing values on it works just like changing values on any other class instance. The difference is that you can persist those changes and, in general, the current state of the class instance (entity) will overwrite the values the row for that instance (entity) had in the database, based on the primary key in the database matching the "id" or similar field in the class instance (entity).

There are exceptions to this behavior, of course, but this is true in general.

http://stackoverflow.com/questions/9778659/what-are-jpa-entities