Originally Posted by Salathe

It's common for many JavaScript libraries to make use of a 'dollar function' as a convenient shortcut for accessing DOM elements (elements in your HTML page). Different libraries do things slightly differently so it's best to look up in the appropriate documentation pages for any particular library that you're using.

It's not a native JavaScript function! Also Google's pretty rubbish at searching for (admittedly very vague) things like that. :)