Leadership is the action of leading a group of people. Or, the actual people who lead the group.
If you think you have leadership skills, you better be able to rally the troops and get the job done. Leadership can be the act of leading, or a name for the group of people doing the leading. The House leadership, newly emboldened by election results, may set an ambitious agenda for the new session of Congress. Your own leadership skills may be called into question if your entire staff resigns and goes to work for your competitor.