how can i resolve this errors

how can i resolve this errors

Hello i get errors alert from firebug can you help me please

ReferenceError: $ is not defined 

$(document).ready(function() {
whmcs.js (ligne 59)
ReferenceError: jQuery is not defined 

jQuery(document).ready(function(){
main.js (ligne 1)
ReferenceError: jQuery is not defined 

jQuery(".domainreginput").hide();