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JavaScript The Definitive Guide 6th Edition, Chapter 1

JavaScript: Names and Versions
JavaScript was created at Netscape in the early days of the Web, and technically, “JavaScript” is a trademark licensed from Sun Microsystems (now Oracle) used to describe Netscape’s (now Mozilla’s) implementation of the language. Netscape submitted the language for standardization to ECMA—the European Computer Manufacturer’s Association—and because of trademark issues, the standardized version of the language was stuck with the awkward name “ECMAScript.” For the same trademark reasons, Microsoft’s version of the language is formally known as “JScript.” In practice, just about everyone calls the language JavaScript. This book uses the name “ECMAScript” only to refer to the language standard.

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JavaScript已经被Sun注册为商标，为了不引起商标权争议，MS使用了JScript这个名称。

我个人喜欢在浏览器中使用时称为JavaScript，在Windows脚本宿主（WSH，Windows Script Host）中使用时称为JScript，以示区别。