Anyone or anything that's still in use, but has been superseded by the next version. The term is often applied to politicians after their successor is elected, but before the incumbent's term ends and he or she leaves office. For a sitting American President, this is the time between losing (or not contesting) a November election and the formal swearing-in of the President-elect the following January. Though still in power, the incumbent has no real mandate to legislate or take any long-term action.