See the documentation
Compass is described as:
Compass is a first class open source Java Search Engine Framework, enabling the power of Search Engine semantics to your application stack decoratively. Built on top of the amazing Lucene Search Engine, Compass integrates seamlessly to popular development frameworks like Hibernate, [and now EclipseLink] and Spring. It provides search capability to your application data model and synchronizes changes with the datasource. With Compass: write less code, find data quicker.
For those of you interested in adding richer search capabilities to your JPA applications you can now combine the capabilities of Lucenewith EclipseLink JPA through the Compass integration.