Hello Friend,
Javascript is the client side scripting code. It is very simple and easy to learn friend. Javascript plays a vital role in the development of the webpages. Without javascript you can't say that you are a full fledged web designer. Take a look at this site which will giveyou easy understanding. http://www.w3schools.com/js/default.asp.
The jscript is the term used by microsoft for "Javascript". The "jquery" is the javascript library and it has it's own api definitions, but it is purely javascript.
Ahamed