EclipseLink is an open-source Java persistence framework that provides a way to manage relational data in Java applications. It is the reference implementation of the Java Persistence API (JPA) and helps developers map Java objects to database tables, making it easier to work with data in a more object-oriented manner. EclipseLink supports various database systems and offers features like caching, lazy loading, and support for complex queries. It is part of the Eclipse Foundation and is widely used in enterprise applications to simplify data access and improve performance.