It refers to aircraft able to take off from a short runway, and land vertically (i.e. with no runway). The most famous example is probably the Hawker Harrier Jump Jet, which though technically a VTOL aircraft, is operationally a STOVL aircraft due to the extra weight it carries at take off for fuel and armaments.
Other examples include:
None of these has reached operational status, though the JSF is expected to enter service by 2010.
wikipedia.org dumped 2003-03-17 with terodump