The Java Development Kit (JDK) is a software development environment used for developing Java applications. It includes tools for compiling, debugging, and running Java programs, as well as libraries and documentation. The JDK is essential for developers who want to create Java-based software. The JDK contains the Java Runtime Environment (JRE), which allows users to run Java applications, and the Java Compiler, which converts Java code into bytecode. It also includes various utilities, such as the Java Virtual Machine (JVM), which executes the bytecode on different platforms, ensuring Java's "write once, run anywhere" capability.