The trouble with the talking about leadership is that we have made a big basket of it, and thrown in anything that looked and smelled like people making other people to do something.
Talking about leadership in general, makes for a great discussion but soon you will be stuck unless you start qualifying and going deeper. Talking about leadership as a generic is as good as talking about fatherhood as a concept. Son you will want to hear more.
In the modern organization that I proposed is ‘powered’ by the Viral Change Platform/operating system , we have at least 4 types of leadership, which I call the 4 hats. This is not a classification of styles or (situational) requirements, but 4 ‘social mobilizing functionalities’
- Hat 1: The hierarchical leadership. The most well known, that positions the leader in a particular ‘network slot’, read, role. This is the top down system that is documented in those organization charts/organograms. This hat is the one you need to wear in order to set guidelines and expectations, inspire, role-model, and ensure performance and reward. This leadership hat dwells in the formal organization.
- Hat 2: Distributed leadership. A relative small number of individuals in the organization are highly connected and have great influence (good or bad). These sometimes called ‘informal leaders’ lead outside the hierarchical lines. They are leaders in their own right even if they have not been formally recognised as such. In the Viral Change™ Operating System, the key is connectivity/influence, and position in the network. We find the Gladwellian classification  of influencers as connectors, mavens or salesmen, intellectually appealing and mostly useless. When these ‘small’ leader community is asked by Hat Ones to get involved, they may receive a label such as Champions, or Change Agents. All labels here (the above plus ambassadors, advocates, etc) have pros and cons. When culturally we are not creating a problem (!) we call them activists. I like the word act within.
- Hat 3. Backstage Leadership™. The distributed engine of leadership represented by the highly connected influencers (tribe) could go on its own. Hierarchical leadership would be foolish to think that it can ignore this distributed leadership. On the contrary, it needs to be nurtured, supported and, dare I say, treated as precious gem inside the tent. This is leadership from the back, backstage, or providing and giving the stage to those with non hierarchical influence. In the Edelman Trust Barometer, horizontal, peer-to-peer, non hierarchical influence and trust is twice as much as that of the CEO. In our own research, the top highly connected (distributed leadership) people in the organization ‘reach out’ twice as much people than the top leadership. (Top Influencers 2, Top Leadership 1 (Hierarchical power in the organization is half of the ‘peer-to-peer’ power) 
- Collective Leadership. This is the collective pull-capability of the organization, the sum of all, the equivalent of the type of horse
power of a car. Strong leadership at the top is not necessarily a condition to have high collective leadership power. Spending considerable amount of time and resources fixing ‘the top leaders’ may be a right thing to do, but may also be a distraction towards creating collective leadership. That the latter follows the former, is a convenient, if weak, assumption.
At least these 4 types need to be recognised and understood, and any Leadership Development Programme that focuses on one of them only, or is biased towards the hierarchical leadership, for example, is not a good Leadership Development Programme for this day and age.