Basic question about $.

Hi

Can someone tell me that the $. means?

For example i am using the Jquery UI widgets and for an object ui.draggable there is a way of addressing a namespace - $.ui.draggable. Sorry - as you can tell I really barely know what I'm asking. - But $. is used by Jquery itself as in $.ajax().

Is ajax() or ui.draggable a property or method of the Jquery object?

Thanks

Kropotkin