JSR223 adds support for scripting languages to run on the Java platform. Any script engine the complies with the 223 spec will be able to run on top of the Java VM.
Why is this important? Think of script as your ‘glue’ – sometimes you need to get component/system/class A to work with B – scripting is an ideal and quick way to integrate and tie together code. It’s also a great quick approach to prototyping apps quickly. By being able to run scripting languages on the Java VM platform, you get the benefits of a statically typed compiled language with the ease of use of a dynamically typed script language.
See this article for further info on JSR223, and check here for a list of 10+ script engines currently supported by JSR223.