Leadership is a special (or natural) ability of Warlords.Erf-b1-p040a It grants all units under direct command of a warlord a bonus.Erf-b1-p084a Leadership also allows the Unit to give orders to units it is stacked with, as well as prevent it from auto-attacking non-allies. Leaders can specify particular enemy units to strike, while ignoring others in the same stack and hex.
Leadership can also refer to a group of leaders, or to a group that have the Leadership ability, wihtout being a reference to the Leadershp ability.
The Leadership Bonus of a Chief Warlord applies to all units of their capital.Erf-b1-p040a A Chief Warlord in the field confers only a partial bonus to all Units in the same hex, but a full bonus to all Units in the stack led by the Chief Warlord.Erf-b1-p113
"Leadership" can also refer to either a single leader or group of leaders such as Warlords or Casters. Gobwin Knob sought to target or "hit" the leadership of the Royal Crown Coalition to deny RCC forces leadership bonuses. They were successful when they hit RCC Leaders Duke Nozzle and the Blue Warlord.