The Java Language Specification (JLS) is a formal document that defines the syntax and semantics of the Java programming language. It serves as a comprehensive guide for developers, detailing how Java programs should behave and how the language features should be implemented. The JLS ensures consistency across different Java compilers and runtime environments. The specification is maintained by the Java Community Process and is updated with each new version of Java. It includes rules for data types, control structures, and object-oriented programming concepts, making it an essential resource for anyone looking to understand or work with the Java language effectively.