The dollar sign is the general jQuery function shortcut. I can’t explain you the complete implementation but it is used, for example, for the DOM node selectors, like:
What you have posted above is a shortcut for the global “DOM ready” function, comparable to classic
$('#example')... // dollar function takes a CSS style selector to address an element in the HTML
window.onload but quicker because it executes scripts inside that function once the DOM is ready which is usually the case before the entire page contents have completely loaded (talk about images). It could also be written out as:
I’m saying “shortcuts” because that’s what it is. The actual function is
jQuery(), e. g. it could all be written as:
The developers just decided to use the dollar sign as shortcut.