A footer bar is a jQuery Mobile toolbar at the bottom of the page. A footer can be positioned at the bottom of the page or "fixed" to the bottom of the screen (so it remains in position when the page is scrolled). A footer can also be configured to show or hide itself when the user taps on the screen.
The standard shipped layouts will provide a footer for you. The footer weblet is only required when creating a custom layout, or using a layout that does not provide one.