What does it mean $ and $$ in javascript?

Please explain the meaning of the $ and $$

This is sample code use $ and $$: https://github.com/cytoscape/cytoscape.js-qtip/blob/master/cytoscape-qtip.js

what mean this code use $:

var $qtipContainer = $('<div></div>');

Answer

The whole code is just a function call with two arguments:

;(function( $, $$ ){ 'use strict';
  // skipped
})(
  typeof jQuery !== 'undefined' ? jQuery : null,
  typeof cytoscape !== 'undefined' ? cytoscape : null
);

The first argument is jQuery global variable (or null, if jQuery is undefined), and the second is cytoscape global variable (or null, if is undefined).