The Apache Jackrabbit content repository is a fully conforming implementation of the Content Repository for Java Technology API (JCR, specified in JSR 170 and 283).

A content repository is a hierarchical content store with support for structured and unstructured content, full text search, versioning, transactions, observation, and more.Apache Jackrabbit is a project of the Apache Software Foundation.

That standard is JSR 170 - Content Repository for Java Technology API (JCR).  JCR is designed to overcome the challenge of proprietary content repositories, helping companies to dramatically reduce costs, while increasing the efficiency and accessibility of their existing content infrastructure.