In jQuery functions, this most often refers to the actual DOM element you're dealing with, whereas $(this) returns a jQuery object that wraps the element.

In JavaScript, this always refers to the current scope. Many of jQuery's functions will set that scope to be the element you're working with.

For instance

$(#someElement).click(function() {

    this;    // the element itself

    $(this); // a jQuery wrapper-object around the element

});

The point is, that the jQuery object has all the jQuery functions (like .detatch() or .prependTo() etc.), while the DOM element is what the browser provides. In the example above, the element would be exactly the same as what you'd get, if you called document.getElementById(someElement)