JavaScript
JavaScript is a language based on ECMAScript. A standard for scripting languages like JavaScript, JScript is ECMAScript. JavaScript is considered as one of the most popular implementations of ECMAScript.
ECMAScript
The full form of ECMA is European Computer Manufacturer's Association. ECMAScript is a Standard for scripting languages such as JavaScript, JScript, etc. It is a trademark scripting language specification.
JScript
JScript released in 1996 by Microsoft, as Microsoft’s dialect of ECMAScript. JScript and JavaScript are different names for the same language. They have different names to avoid trademark issues.