I have been going through some jQuery functionality.
Can any one please give me some idea of what the difference is between the use of $ and $$
jQuery is an object provided by jQuery. $ is another, which is just an alias to jQuery.
$$ is not provided by jQuery. It's provided by other libraries, such as Mootools or Prototype.js.
More importantly, $$ is also provided in the console of modern browsers as an alias to document.querySelectorAll. Except if it's overridden by another library. $ is also provided in the same way, as an alias to document.querySelector.
See this answer for more information.