I use the term “role” to refer to someone with the title of leader in their organization. I use the term “function” to refer to the act of leadership – influencing others to take a certain action. It is possible that someone might have the title of leader (which is their role) but not provide any real leadership for their team. Someone on the team might not have the title of leader, but others respect and listen to that person. That person functions as a leader, even though they don’t have an official title.