Use jQuery.noConflict() can be compatible with other js library
Use jQuery.noConflict() redefine default selector of jquery, yes, it's "$".
You can rename $j(), $jQuery()...
But, before use jQuery.noConflict(), other js library must be loaded.
For example:
var $j = jQuery.noConflict();
$j(document).ready(function(){
$j("#btn").click(function(){
$j(this).hide();
})
});