Object-Relational Mapping (ORM) is a technique that allows you to fetch and manipulate from a database by using an object-oriented programming paradigm. ORM is really nice for programmers because it relies on object-oriented concepts, not on database structure. It also makes development much faster and reduces the amount of source code. ORM is mostly independent of the databases and developers don't have to worry about vendor-specific SQL statements.

Java Persistent API (JPA) provides object-relational mapping for Java developers. The JPA entity is a Java class that presents the structure of a database table. The fields of an entity class present the columns of the database tables.

Hibernate is the most popular Java-based JPA implementation, and it is used in Spring Boot as a default. Hibernate is a mature product and it is widely used in large-scale applications.