This is a tough question to answer without dipping into platitudes. Try sharing leadership examples instead. Say, "The best way for me to answer that is to give you a few examples of leadership challenges I've faced..." and then share situations where you dealt with a problem, motivated a team, worked through a crisis... explain what you did and that will give the interviewer a great sense of how you lead.

And, of course, it lets you highlight a few of your successes.