Java SE Development Kit 8, also known as JDK 8, is a software development kit provided by Oracle Corporation for developing Java applications. It is a major release of the Java Platform, Standard Edition (Java SE). JDK 8 was a significant update with many new features and improvements compared to its predecessors.

Some key features introduced in JDK 8 include:

1. Lambda Expressions: A new way to write anonymous functions, making it easier to work with collections and streams.
2. Stream API: The Stream API allows for functional-style operations on collections, providing a more concise and expressive way to manipulate data.
3. Date and Time API: A new date and time API that replaces the older java.util.Date and java.util.Calendar classes, offering better functionality and safety.
4. Nashorn JavaScript Engine: A modern JavaScript engine for the JVM, allowing developers to execute JavaScript code from Java applications.
5. Default Methods: The ability to add default method implementations to interfaces without breaking compatibility with existing implementations.
6. Compact Profiles: A set of predefined subsets of the Java SE Platform that allow for more efficient use on embedded and resource-constrained devices.
7. PermGen Removal: In JDK 8, the permanent generation (PermGen) was removed and replaced with a more flexible Metaspace for class metadata storage.
8. Improved Security: Enhancements in security features, such as the introduction of the SSL/TLS Server Name Indication (SNI) extension and the Crypto Algorithms property.

JDK 8 was a long-term support (LTS) release, which means it received updates and bug fixes for an extended period, making it a popular choice for many enterprise applications.