Leadership is an influence relationship among leaders and followers who intend real changes that reflect their mutual purposes.
Leadership is the name that people use to make sense out of complex events and the outcomes of events they otherwise would not be able to explain. In other words, people attribute leadership to certain individuals who are called leaders because people want to believe that leaders cause things to happen rather than have to explain causality by understanding complex social forces or analyzing the dynamic interaction among people, events, and environment.
In leadership writ large, mutually agreed upon purposes help people achieve consensus, assume responsibility, work for the common good, and build community.
Bad leadership is an oxymoron.