What does “portable application” mean?

Question

I am reading java persistence specification version 2.1 There is last paragraph in 25 page:

Entity subclasses may override the property accessor methods. However, portable applications must not override the object/relational mapping metadata that applies to the persistent fields or properties of entity superclasses.

So what does "portable applications" mean? Could somebody explain and provide a few exmaples?

Answer 1

JPA is a specification. Multiple implementations of this specification exist: Hibernate, EclipseLink, etc. A portable application is an application that is written to work with any of these implementations.