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JPA (Java Persistence API) is a Java specification for object-relational mapping (ORM) that allows developers to work with databases using Java objects. JPA provides a set of annotations that can be used to map Java classes to database tables, and it also provides an API for querying and manipulating data.

When working with JPA, you can use JPQL (Java Persistence Query Language) to write queries that are database-agnostic and can be translated to SQL by the JPA provider. JPQL is similar to SQL, but instead of operating on tables and columns, it operates on entities and their attributes.

Here's an example of using JPQL to query for all employees with a salary greater than 50000:

TypedQuery<Employee> query = entityManager.createQuery(
    "SELECT e FROM Employee e WHERE e.salary > 50000", Employee.class);
List<Employee> employees = query.getResultList();

This JPQL query selects all `Employee` entities where the `salary` attribute is greater than 50000. The `entityManager` object is an instance of `javax.persistence.EntityManager`, which is responsible for managing JPA entities and transactions.

When the query is executed, the JPA provider (such as Hibernate or EclipseLink) will translate the JPQL query to SQL and execute it against the database. The result is returned as a list of `Employee` objects.