OpenJDK (Open Java Development Kit) is an open-source implementation of the Java Platform, Standard Edition (Java SE). It is a free and community-driven project that provides a reference implementation of the Java platform.

Here are some key points about OpenJDK:

1. Open Source: OpenJDK is released under an open-source license, which allows anyone to view, modify, and distribute the source code. This openness promotes transparency and community collaboration.

2. Java Standard Edition: OpenJDK focuses on implementing the Java SE specifications, which define the core Java platform, including the Java Virtual Machine (JVM), standard libraries, and the Java programming language itself.

3. Compatibility: OpenJDK aims to be compatible with the official Oracle JDK (Java Development Kit). It strives to provide the same functionality and adhere to the same Java standards as the Oracle JDK.

4. Version Support: OpenJDK supports multiple versions of Java, including Java 8, Java 11 (LTS – Long-Term Support), Java 17 (LTS), and other intermediate releases. Users can choose the version that suits their application’s requirements.

5. Community Collaboration: OpenJDK development is collaborative and involves contributions from individuals, open-source organizations, and commercial entities. This collaboration helps improve the quality and stability of the Java platform.

6. Adoption: Many Linux distributions and cloud providers offer OpenJDK as the default Java runtime environment. This makes it readily available for developers and users in various environments.

7. Builds and Distributions: OpenJDK provides a source code repository from which different organizations and projects create their own OpenJDK builds and distributions. Examples include Oracle JDK (based on OpenJDK), Adoptium (formerly AdoptOpenJDK), Amazon Corretto, and others.

8. TCK Compatibility: To ensure compatibility with the Java SE specification, OpenJDK implementations are rigorously tested against the Java Technology Compatibility Kit (TCK).

9. Security Updates: OpenJDK receives security updates and patches to address vulnerabilities, just like other JDK distributions.

10. Multi-Platform: OpenJDK is available for various operating systems, including Linux, Windows, macOS, and others, making it versatile and suitable for different development environments.

To use OpenJDK, you can download it from the official OpenJDK website or obtain it from a package manager or distribution specific to your operating system. The choice of OpenJDK version depends on your application’s compatibility requirements and whether you need a long-term support (LTS) version or an intermediate release.