Differences between CSS3 :hover and :focus?

Hover is 'true' when the mouse pointer is over an element. Focus is true if the cursor is in that element. It's possible for hover to be false and focus true (e.g click in a text field then move the mouse away)

:hover applies to any element that the mouse cursor is currently over. :focus refers to form focus, and is the current form element with focus. Roughly speaking, if you start typing, which element will you be filling?