Your ability to command and lead others, Leadership is most useful for military men, politicians, reformers and the like. It encompasses the ability to inspire others through oratory, dramatic gestures, bearing, and force of personality.
Poor - You follow, not lead
Average - Allows you to manage a small business successfully, or to lead troops in peacetime situations.
Good - You can lead troops into battle and have them trust your judgment
Great - You have a small reputation as a leader; people will follow you just on the strength of your name.
Exceptional - You can lead armies into battle and inspire people to doe their very best (and improve their Abilities at the specific task you need them to do by 1 Rank)
Extraordinary - Like Bismark or Grant; their men will go to Hell and back for them, and their very presence inspires their followers to do impossible things (improving their Abilities at the specific tasks you need them to do by 2 Ranks)