Java Development Kit (JDK) is a software development environment used to create Java applications and applets. It contains tools such as the Java compiler, Java interpreter, Java debugger, and other related tools that are essential for Java programming. JDK is widely used by developers to create and deploy applications on various platforms such as desktops, servers, and mobile devices. Knowledge and proficiency in JDK are important for Java developers to build scalable, secure, and robust applications.