What are the rules for $() ?

What are the rules for $() ?

Hello, I am jquery noob.
I understand that $('p') would return all the p elements. But what happens when you put two parameters in the the $() ?
Please take a look at the code below. I got it from http://nettuts.com/tutorials/javascript-ajax/inettuts/
I understand what it's doing but I don't understand why it's doing it or what the rules are.

// Loop through each widget within the columns: 
    $(settings.widgetSelector,$(settings.columns)).each(function (i) { 


Note: setting.widgetSelector and setting.columns are variables that hold the values '.widget' and '.column'[/url]

Many thanks in advance.