JavaScript
JavaScript is a scripting language developed by Netscape Communications designed for developing client and server Internet applications. Netscape Navigator is designed to interpret JavaScript embedded into Web pages. JavaScript is independent of Sun Microsystem's Java language.
JScript
Microsoft JScript is an open implementation of Netscape's JavaScript. JScript is a high-performance scripting language designed to create active online content for the World Wide Web. JScript allows developers to link and automate a wide variety of objects in Web pages, including ActiveX controls and Java programs. Microsoft Internet Explorer is designed to interpret JScript embedded into Web pages.
The biggest difference now between JavaScript and JScript are all of the additional commands that JScript supports that allow access to ActiveX and the local computer. These commands are intended for use on intranet sites where you know the configuration of all of the computers and that they are all running Internet Explorer.
There are still a few areas remaining where JavaScript and JScript differ in the means that they provide to perform a particular task. Except in these situations the two languages can be considered to be equivalent to one another and so unless otherwise specified all of the references to JavaScript that you see will also usually include JScript.