Peter, thanks for jumping in!  I agree that many traditionally use the word leader in conjunction with authority.  I also agree that leadership can be demonstrated by anyone at any level.  Thus, indeed, it makes them a leader.

I enjoy attempting to "push the envelope" by asserting that because we can all demonstrate leadership, we can all be called leaders.  Of course, some people's leadership responsibilities are far greater and impactful than others.  That said, at the end of the day, we all have the ability to influence others, and we can take responsibility to make that the best influence we're personally able to bring.