What's namespace in JavaScript and how to export method from namespace?

Please check this link for my complete code (It's simple though)

Question 1: What's the namespace defined in JavaScript? From my understanding, it looks like that any object can be an namespace?

Say we have a namespace called 'SPA', which means "Simple Page Application", inside this namespace, I define four module scope variables, $chatSlider, $toggleSlider, $onclickSlider, initModule;

var spa = (function( $ ) {
    // Module scope variables
    var
    // Set constants
        configMap = {
            // some code here
        },

        // Declare all other module scope variables
        $chatSlider, toggleSlider, onClickSlider, initModule;

    toggleSlider = function() {
        // some code here
        }
        // do not take action if slider is in transition
        return false;
    }

    onClickSlider = function(event) {
        toggleSlider();
        return false;
    }

    // Public method / initModule/ 
    // sets initial state and provides feature

    initModule = function($container) {
       // some code here
        return true;
    };

    return {
        initModule: initModule
    };
})(jQuery);

And now I want to call initModule outside "spa", like this 

$(document).ready(function () {
    spa.initModule( $('#spa'));
});

Question 2: why we have to write 

return {
    initModule: initModule
};

To me, return {initModule} seems make more sense, what does the code above mean, what's the syntax of it?

Last but not least, usually I write function in the format like 

function ( $var) {
   // function code here
}

So what does this $ and jQuery mean here 

function( $ ) {

}(jQuery)

What's the namespace defined in JavaScript?

Namespace isn't a piece of terminology defined by the language. It's common usage just means "An object, assigned to a global variable, to which all public functions for a piece of code are assigned so they can be exposed globally while only using a single global variable".

why we have to write return { etc etc

Otherwise the immediately invoked function expression (IIFE) will return undefined. The return value is what is assigned to the global variable (spa).

You need it to be an object.

The left hand side of the : is the property name, the right hand side is the value (which is the previously declared local variable which happens to have the same name as the property).

return {initModule} seems make more sense

That's a syntax error in JavaScript. An object consists of a set of property/value pairs.

So what does this $ and jQuery mean here

$ is the name of the argument in the function expression definition.

jQuery is the value passed as the first argument when that function is called (which is immediately).