STOVL is an acronym for Short Take Off and Vertical Landing.
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. Ditto for the F-35 Joint Strike Fighter, which demonstrated VTOL capability in test flights but is operationally STOVL.
Other examples include: