The cash sign is just an alias for the jQuery function. Starting the variable name with $ has no effect on that variable. It is customary though, especially in jQuery plugin development, to use variables already wrapped in jQuery with a cash sign, so you know you can call jQuery methods, without having to wrap them.
In jQuery the variable is assigned a copy of the jQuery function. This function is heavily overloaded and means half a dozen different things depending on what arguments it is passed.
A '$' in a variable means nothing special to the interpreter, much like an underscore. From what I've seen, many people using jQuery (which is what your example code looks like to me) tend to prefix variables that contain a jQuery object with a $ so that they are easily identified and not mixed up with, say, integers. The dollar sign function $() in jQuery is a library function that is ...
What are the possible reasons for document.getElementById, $("#id") or any other DOM method / jQuery selector not finding the elements? Example problems include: jQuery silently failing to bind an event handler jQuery "getter" methods (.val(), .html(), .text()) returning undefined A standard DOM method returning null resulting in any of several errors: Uncaught TypeError: Cannot set property ...
Why does jQuery or a DOM method such as getElementById not find the ...
It is shorthand for jQuery (). Which you can use if you want. jQuery can be ran in compatibility mode if another library is using the $ already. Just use jQuery.noConflict (). $ is pretty commonly used as a selector function in JS. In jQuery the $ function does much more than select things though.