jQuery issue Uncaught TypeError: jQuery(...).countdown is not a function

Hello, im getting this jQuery error in my console log in a localhost -

Uncaught TypeError: jQuery(...).countdown is not a function at theme.js:3

The actual code is

jQuery('#clock').countdown('2020/10/10', function(event) {
	  var $this = jQuery(this).html(event.strftime(''
	    + '<span>%w</span> weeks '
	    + '<span>%d</span> days '
	    + '<span>%H</span> hr '
	    + '<span>%M</span> min '
	    + '<span>%S</span> sec'));
	});

Whats wrong with my code?