Originally called JavaScript, this is not a sort of "interpreted Java". It is, instead, a dynamically-typed scripting language with syntax similar to that of Java and C++ .
It is commonly used to run client-side logic in web applications. Unfortunately, this too often leads to security risks; "Bad Guys" often abuse it for evil, with the result that many people prefer to browse the web with support for this language turned off. This doesn't entirely work out, as web frameworks are increasingly depending on its availability for client-side functionality.