Java Persistence API (JPA) is a specification of Java that describes the management of relational data in enterprise Java applications. It is a collection of classes and methods to persistently store vast amounts of data into a database. JPA acts as a bridge between object-oriented domain models and relational database systems. It is not a tool or framework by itself, but rather a set of concepts that guide implementers. JPAs object-relational mapping (ORM) model was originally based on Hibernate, but it has since evolved. JPA is used to reduce the burden of writing codes for relational object management. It allows easy interaction with a database instance and provides a repository abstraction that is a key building block of domain-driven design based on the Java application framework Spring.

JPA requires an implementation to use, and ORM tools like Hibernate, TopLink, and iBatis implement JPA specifications for data persistence. While JPA was originally intended for use with relational databases, some JPA implementations have been extended for use with NoSQL datastores. Popular JPA implementations like Hibernate and EclipseLink now support JPA 3.

In summary, JPA is a specification of Java that provides a collection of classes and methods to persistently store data into a database. It acts as a bridge between object-oriented domain models and relational database systems and requires an implementation to use. ORM tools like Hibernate, TopLink, and iBatis implement JPA specifications for data persistence.